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==Using this page==
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{{Tocright}}
The 'Contents' box above contains a list of available functions roughly grouped by usage scenario, and each function name gives a fair indication of what it might do. Each of the group headers contain some basic information pertinent to the functions inside the group. Click on a function or function group header in the Contents box to be taken directly to more information about it on the page. At the bottom right of each section there is a "Back to top" link which will take you back up to the Contents box allowing you to quickly get to where on the page you would like to go next.<br>Some of the function descriptions reference other functions to help illustrate their usage. Where this happens, a link to the referenced function is provided if needed. The browser's "Back" button will then return you to the previous place you were at on the page.<br>The page contains some references that link to external pages. Such links can be identified by the little square icon that follows them, [http://yabb.jriver.com/interact like this--->]. These links will not load in new tabs or windows, so, if you would like to keep this page open in your browser, right click on these links and choose to open them in a new tab or window.<br><div style="text-align:right;">([[#top|Back to top)]]</div>
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Media Center provides a simple programming language that enhances and enriches its overall user interface and usability.
==Overview==
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This language, commonly called the expression language, is simple to learn, simple to use, and can greatly enhance your experience using Media Center.
  
The J. River Media Core database engine supports Excel-style functions for use in view schemes, searches, displayed columns, and tag editing.
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Expressions are ubiquitous throughout Media Center, used in areas such as:
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:* The categories in a view
 +
:* File list expression columns
 +
:* Theater View
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:* Customized view headers, grouping and sort criteria
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:* The library field manager (fields with data type Calculated data)
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:* File and folder location definitions
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:* Auto-import rules
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:* Custom DLNA titles
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:* The player's display
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:* Captions and thumbnail text
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:* The link manager (expressions help format link URLs)
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:* Rename, Move, & Copy tool
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:* Tag assignment
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:* Complex search queries
  
An expression is a mixture of text, fields, and functions. A function allows special operations to be performed. Functions are all listed with a name followed by an opening and closing parenthesis. When building expressions, the instructions you wish to pass to the function are placed inside these parenthesis, with multiple instructions separated by commas. When your expression is evaluated, any spaces entered after a comma are ignored. This allows you to compose complex expressions on multiple lines, making it easier to keep track of where you are in your expression. Occasionally, you will find that you want a space, or parenthesis character to be treated literally as part of your instructions, rather than expression syntax, and in these cases, the character is "escaped" by using a preceding forward slash. Examples using this escaping can be seen [[#Clean(...): Returns a cleaned up version of a filled in template|here]] and [[#Replace(...): Replace or remove strings from a value.|here]].
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An expression is a mixture of ordinary text, pre-defined functions, and a few reserved characters and constructs that have special meaning. An expression is evaluated by Media Center's expression engine and textual output is produced. This output is then used by Media Center to customize the user interface and affect its method of operation.
As you progress with your expression building, you will begin nesting multiple functions into a single expression; always remember that a completed expression must contain a matching number of opening and closing parenthesis in order to work reliably.
 
  
The functions available to us range from highly functional, with a broad range of applicable uses, through specialised, limited use functions that only appeal to a select group of users, to seemingly redundant functions and obscure functions that MEDIA CENTER uses internally. The functions below are listed with those with the broadest appeal at the top, and the more obscure at the bottom.
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== The Anatomy of an Expression ==
  
<ins>'''Any given expression can only work on any given single file.  It is not possible to compare a field in one file with a field in another file.'''</ins><br>
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As mentioned above, an expression is a mixture of text and function calls (and some reserved stuff described shortly).
Batch file operations are possible, and when used in a list, even a grouped list, an expression will be applied to each individual file in turn, not as a group.
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The simplest expression would be some basic, literal text, such as <span style="font-family: monospace,monospace; font-size:1em;">A good movie</span>.
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The expression engine evaluates this expression, finds nothing special, and then outputs the result: <span style="font-family: monospace,monospace; font-size:1em;">A good movie</span>.  Simple.
  
A slightly extended overview  is also available elsewhere in this wiki, titled [http://wiki.jriver.com/index.php/Database_Expressions Database Expressions], and another page attempts to demonstrate MEDIA CENTER mimicking the [http://wiki.jriver.com/index.php/Database_Expressions_AND_OR_And_XOR "AND",&nbsp;"OR"&nbsp;and&nbsp;"XOR"] database searches.
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But simple text only has so much utility.
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The ability to transform or generate content is much more interesting and useful.
 +
And this is when [[#Functions|functions]] are employed.
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Media Center [[#Function Index|provides many functions]], which when called, produce some output.
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Most functions require some form of input, called arguments, and most functions generate output.
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By supplying a function with various arguments, the function will return some output value which is just more text.
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And this output text can be the used by other functions, and so on.
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Each function has a unique name, and calling upon a function to do some work requires little more that using its name anywhere in the expression.
  
<div style="text-align:right;">([[#top|Back to top)]]</div>
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A function call looks like this:
==When, Where and How to use expressions==
 
The use of expressions in MEDIA CENTER can be broken into three distinct categories:
 
  
* [[#Tag or filename editing|Tag or filename editing.]] ('''''<ins><span style="color:red">Data is physically altered by the expression</span></ins>''''')
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:{{monospace|<i>functionname</i><b>(</b><i>argument 1</i>, <i>argument 2</i>, ...<b>)</b>}}
* [[#Filtering a list of files using a search rule|Filtering a list of files using a search rule.]] (''No data is altered'')
 
* [[#Change how existing data is displayed|Change how existing data is displayed.]] (''No data is altered'')
 
  
The implementation of the expression differs between each of these three categories, differences which are outlined below.
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The syntax of the function call is the function's case-insensitive name, immediately followed by an opening parenthesis character, one or more comma-separated arguments, and a closing parenthesis character.
<div style="text-align:right;">([[#top|Back to top)]]</div>
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Whitespace after the commas is optional, but helps readability and formatting.
====Tag or filename editing====
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And each argument itself is also just an expression. And some arguments are optional.
Expressions can be used to simplify the batch editing of file tags, or if required, physical filenames too. It is important to remember that when using expressions in this way, file tags are physically altered, and if the expression is applied to a "filename" field, then the physical name or path of the file will be changed on the hard drive.<br>
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If an argument is optional, it can be omitted and its default value will be used.
Expression functions that are typically used for these kind of tasks are grouped together in the [[#Functions for filename and field manipulation |list of functions]]. The grouping is provided as a rough guide only, as any function that gets the job done can be used.<br>
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If the argument is omitted, a comma-separator will still be required if additional arguments follow.
When using expressions for this kind of task, the expression is either entered into the tag window, or by using inline editing in the file list, and a preceding "=" sign must be inserted to instruct the tagging engine to invoke the expression evaluator, rather than apply the expression as physical tag data. The following screen pictures will help to illustrate using expressions in this way:<br>
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The following example uses the [[String_Manipulation_Functions#FixCase|FixCase()]] function to change its input to Title Case:
{| align=center
 
|-
 
|
 
[[image:Inline1.png|frame|Pressing "Enter" copies the Date data into the caption field]]
 
|
 
[[image:Inline2.png|frame|Just like that!]]
 
|}
 
  
Next, using the [filename (name)] field and expressions to directly edit the file name on the hard disk:
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:{{monospace|fixcase(A good movie)}}
{| align=center
 
|-
 
|
 
[[image:Inline4.png|frame|Pressing "Enter" renames and renumbers the selected files]]
 
|
 
[[image:Inline5.png|frame|Just like that!]]
 
|}
 
''Worth noting that any mistakes made using expressions in this way can be undone by pressing '''Ctrl+Z'''''
 
<div style="text-align:right;">([[#top|Back to top)]]</div>
 
====Filtering a list of files using a search rule====
 
Expressions can be used as search filters, and in order to do so, the expression must be entered into the search field using the following format:<br>
 
'''[=EXPRESSION]=1''' or '''[=EXPRESSION]=0'''
 
  
All files that match the expression will return "1" and all that don't match, return "0". Decide which is required and use "1" or "0" accordingly.
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The result is <span style="font-family: monospace,monospace; font-size:1em;">A Good Movie</span>.
  
Remember that the search field appears in many places throughout MEDIA CENTER, places that include:
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A slightly more complex expression example consists of both text and a nested function call:
* The search field itself (in the top right corner of the program)
 
* A view scheme search list
 
* "Edit Files To Show" area of the Customize View dialogue
 
* Play Radio Files
 
* The last.fm submission filter
 
* The links manager
 
and this method of expression application can be used in all of them.
 
  
An example of an expression formatted for use in the search field would be:
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:{{monospace|Wow! fixcase(replace(A good movie, good, great))}}
'''<span style="color:blue">[=<ins>[[#IsEqual(...): Compares two values in one of nine specified modes|isequal]]</ins>(<ins>[[#FormatDate(...): Formats a date value in a specified manner|formatdate]]</ins>([date&nbsp;imported,0],MM//yyyy),formatdate(<ins>[[#Now(...): Retrieve and display the system date|now()]]</ins>,MM//yyyy),1)]=1</span>'''
 
Which will list all files that have been imported this month.
 
<div style="text-align:right;">([[#top|Back to top)]]</div>
 
====Change how existing data is displayed====
 
As well as the search field detailed above, expressions can also be used in many other places within MEDIA CENTER. Places that you might consider using expressions include:
 
  
* The player information bar (right click the information bar, choose "Customize")
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Inner functions are called before outer functions, so the [[String_Manipulation_Functions#Replace|Replace()]] function is call first:
* The image playback caption
 
* The "Rename, Move or Copy Files" tool
 
* Panes (''aka categories'')
 
* List columns (right click a column header and choose "Add expression column" from the menu)
 
* Thumbnail text
 
* The library field manager (''Create expression based library fields'')
 
* Theatre View
 
* The links manager (''Use expressions to format the URLs for your links'')
 
  
To give usage examples for all of these locations is beyond the scope of this page, so a few tips should suffice to get those interested up and running.
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:{{monospace|replace(A good movie, good, great)}}
  
* For photos and videos, thumbnail text can be extremely useful, with the slight drawback that space there is a bit on the limited side. Using expressions here can be very productive indeed, for example, by using expressions, it is possible to instruct MEDIA CENTER to only display selected data if it actually exists, effectively getting rid of any of those "unknown ..." entries in the list.
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and its output is then supplied as the input to the [[String_Manipulation_Functions#FixCase|FixCase()]] function.
* Expressions can be used in link properties (accessed via the link manager) so that a link will only be displayed if certain criteria are met, helping to keep the links bar uncluttered, populated with just those links that pertain to the current file list or selection. [http://yabb.jriver.com/interact/index.php?topic=59322.0 This topic] contains a couple of interesting "Link Manager" tips that some might find useful.
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[[String_Manipulation_Functions#Replace|Replace()]] does its work substituting {{monospace|good}} with {{monospace|great}}, and returns {{monospace|A great movie}}.
* Some users choose to keep media files stored on drives, or in paths, dependent upon media type. The "Base path", "Directory" and "Filename" fields in the "Rename, Move or Copy Files" all accept expressions, offering the user powerful control over how the tool deals with files, dependent upon how they are tagged.
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This output is then supplied as the argument to [[String_Manipulation_Functions#FixCase|FixCase()]] which sees only the text {{monospace|A great movie}} (it knows nothing about how it was produced).  So the function call:
* Expressions can be saved as library fields in their own right. See [[Changing_the_number_of_plays|Editable expression fields]] and this [http://yabb.jriver.com/interact/index.php?topic=54226.msg374211#msg374211 "Eureka moment"] for a couple of related tips.
 
<div style="text-align:right;">([[#top|Back to top)]]</div>
 
==Specify data types for expression based fields==
 
Now and again (or always, in the case of "[[#Functions for the manipulation and creation of list type fields|List type]]" expressions), an expression based pane or library field may not sort correctly, or rather, may not sort as desired. Think about things like months... should they be sorted alphabetically or chronologically? They will sort alphabetically by default, so no problems there, but, if a chronological order is required, then a "Data Type" for the expression must be specified. Data types are set by appending the following string to an expression: '''&datatype=[<span style="color:blue">''DATA TYPE''</span>]''', where <span style="color:blue">''DATA TYPE''</span> is one of the following five values:
 
  
* '''List''': ''A list of strings, separated by semicolons''
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:{{monospace|fixcase(A great movie)}}
* '''String''': ''Sorts as strings (with smart number handling)''
 
* '''Number''': ''Sorts values as numbers (decimal or integer)''
 
* '''Path''': ''Sorts using a smart filename compare style''
 
* '''Month''': ''Sorts string month names (i.e. January, February, etc.)''
 
  
The following screen images show these data type instructions in action:
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in turn outputs {{monospace|A Great Movie}}.
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Now that the functions have produced their output, the final output, including the literal {{monospace|Wow!}} leading text is
  
{| align=center
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:{{monospace|Wow! A Great Movie}}
|-valign=top
 
! colspan="2" style="background: #ecfeea; color: black; border: 1px solid black" | &DataType=[Month]
 
!
 
! colspan="2" style="background: #ecfeea; color: black; border: 1px solid black" | &DataType=[List]
 
|-valign=top
 
|
 
[[image:Datatype1.png|left|frame|Used in a pane, '''formatdate([date,0],MMMM)''' returns the months as requested, but the alphabetic order is a little confusing.]]
 
|
 
[[image:Datatype2.png|right|frame|Adding the "month" data type, like so, '''formatdate([date,0],MMMM)&datatype=[month]''', takes care of the order.]]
 
|width=100|&nbsp;&nbsp;&nbsp;
 
|
 
[[image:Datatype3.png|left|frame|No data type has been specified, so the expression results are presented literally, as individual string values.]]
 
|
 
[[image:Datatype4.png|right|frame|Add the "list" data type to the expression and it is then formatted correctly in the pane. Here, the [[#ListBuild(...): Build a list from a series of values|ListBuild]] function has been used to create a nested browsing tree.]]
 
|}
 
<div style="text-align:right;">([[#top|Back to top)]]</div>
 
==Fields==
 
  
Any text between brackets [] will be replaced with the corresponding field from your library. As an example, [Artist] would be replaced by Bob Dylan for any Bob Dylan tracks. If the text between brackets doesn't match any known fields, it will be left alone, [My Fake Artist] will be treated literally, square brackets and all.  After the field name, a comma can be placed followed by a 0 or 1 to indicate whether the field should be formatted. So, [Duration] and [Duration, 1] will give "4:02" while [Duration, 0] will give "242". This is particularly important when working with the "Format" functions, where most times you will want the evaluator to work with the raw field contents rather than the formatted contents you see in the file list.
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== Fields ==
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The expression examples thus far have been limited to static literal text.
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Expressions have much more utility when they use data from other sources, such as a file's metadata.
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Media Center maintains this metadata in its defined fields.
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This data is accessed using the [[Accessing_and_Storing_Functions#Field|Field()]] function, and its first argument is the case-insensitive name of the field to be accessed.
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For example, the function call <span style="font-family: monospace,monospace; font-size:1em;">field(album)</span> will return the current* file's value for the album field (* more will be said later about the current file).
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If the album field contained the value <span style="font-family: monospace,monospace; font-size:1em;">After Hours</span>, the expression:
  
Function and field values in expressions are ''not'' case-sensitive.
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<div style="margin-left: 20pt"><span style="font-family: monospace,monospace; font-size:1em;">fixcase(field(album), 3)</span></div>
Available functions with descriptions and examples are listed below.
 
<div style="text-align:right;">([[#top|Back to top)]]</div>
 
==Functions==
 
  
===If(...): Ask closed questions and control output dependent upon result.===
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would produce <span style="font-family: monospace,monospace; font-size:1em;">AFTER HOURS</span>.
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First <span style="font-family: monospace,monospace; font-size:1em;">field(album)</span> is evaluated, returning <span style="font-family: monospace,monospace; font-size:1em;">After Hours</span>.
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The [[String_Manipulation_Functions#FixCase|FixCase()]] function is supplied with this output as its first argument, and its second argument is <span style="font-family: monospace,monospace; font-size:1em;">3</span>, which happens to specify that it should perform upper-casing.
  
{| style="width: 100%; border: 1px solid black" align="top" border="1" cellpadding="3"
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Because fields are so frequently used in expressions, an abbreviated form called [[square bracket notation]] exists for accessing their values. This makes it easier to both read and write expressions.
|- valign="top"
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Nonetheless, both forms are equivalent.
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" width=100 | If()
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The abbreviated form is simple: immediately surround the field's name with opening and closing square brackets, for example, <span style="font-family: monospace,monospace; font-size:1em;">[album]</span>.
| style="background: #ecfeea; color: black; border: 1px solid black" width=1200 | This will be the function you will likely use more than any other. It is typically used in conjunction with one or more other functions and allows you to give specific instructions depending upon whether the result is positive (1) or negative (0). The positive instruction is always given first.
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The previous example is now written more simply as:
|- valign="top"
 
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Construction
 
| style="background: #ecfeea; color: black; border: 1px solid black" | '''if(''expression to test'',instructions if positive,''instructions if negative'')'''
 
|- valign="top"
 
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Examples
 
|style="background: #ecfeea; color: black; border: 1px solid black" | '''if(isequal([artist],bob dylan,1),Genius,Mediocre)'''<br>''Wherever this expression is applied, be it as an expression column or category, as part of a renaming rule, thumbnail text, if the artist tag is Bob Dylan, MEDIA CENTER will produce Genius, and for all other artists, it will produce Mediocre.'' The "IsEqual()" function is described in the first table below.
 
<br>
 
'''if(isequal([artist],bob dylan,1),Genius,if(isequal([album],Joshua Tree,8),Great Album,Mediocre))'''
 
<br>''Here, we have two nested "If" functions. First we ask if the artist is Bob Dylan, if the result is positive, write "Genius". If the artist is not Dylan, we then ask if the album is "Joshua Tree", if yes, write "Great Album", and if no, write mediocre''
 
  
<br>On it's own, "If()" is rather boring and not a lot of use. When used in conjunction with other functions, however, it becomes very powerful indeed. In the two examples above, the numbers 1 and 8 have been used. These are comparison mode switches used by the IsEqual function. There are 9 different compare modes in total, all of which are detailed below. Note how the second example ends with two closing parenthesis, one for each "If" function.
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<div style="margin-left: 20pt"><span style="font-family: monospace,monospace; font-size:1em;">fixcase([album], 3)</span></div>
|}
 
<div style="text-align:right;">([[#top|Back to top)]]</div>
 
  
===Query, Test and Compare using "Is" Functions===
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=== Field Values ===
All of the functions in this section, when used on their own, will only ever return one of two values, 1 (true) or 0 (false). There is a "[[#FormatBoolean(...): Formats a boolean (true / false) value in a specified manner|FormatBoolean()]]" function that can be wrapped around these and allows us to specify the output for each case and is discussed in more depth in the Format section. The real power and versatility of these "Is" functions is released when they are wrapped inside the If() function discussed above.
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For the sake of simplicity and clarity, the section above glossed over an important detail regarding how
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Media Center outputs field values.
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Recall that [[Accessing_and_Storing_Functions#Field|Field()]] is the function used to return the value of a specified field.
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But [[Accessing_and_Storing_Functions#Field|Field()]] also has a second argument that indicates the format of the value that it returns.
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Because field values are used in a variety of situations, the [[Accessing_and_Storing_Functions#Field|Field()]] function can produce output suitably formatted for the requirements.
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There are two forms of output: one is a nice, friendly human-readable format suitable for use in views or other display locations; the other is a raw format which returns the representation stored internally by Media Center which is useful when uninterpreted values are necessary.
  
====IsEqual(...): Compares two values in one of nine specified modes====
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By default, Media Center <i>always</i> outputs the friendly format, so expressions sometimes need to take this into account and chose the format accordingly.
{| style="width: 100%; border: 1px solid black" align="top" border="1" cellpadding="3"
 
|- valign="top"
 
! scope="row" style="white-space:nowrap; background: #A8E4A0; color: black; border: 1px solid black;" width=100 | IsEqual()
 
| style="background: #ecfeea; color: black; border: 1px solid black" width=1200 | Compares two values in one of nine specified modes ("exact match", "Is greater than" etc.) and outputs 1 for a positive match and 0 for a negative match. If no compare mode is specified, the compare will default to 0.
 
|- valign="top"
 
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Construction
 
| style="background: #ecfeea; color: black; border: 1px solid black" | '''isequal(''1st value to compare'',2nd value to compare'',compare mode)'''
 
  
''Available Compare Modes:''
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Not used earlier because it is optional, the second argument to the [[Accessing_and_Storing_Functions#Field|Field()]] function selects the mode of output:
* 0: ''case-sensitive string compare for equality''
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the value <span style="font-family: monospace,monospace; font-size:1em;">0</span> selects the raw mode, and the default value of <span style="font-family: monospace,monospace; font-size:1em;">1</span> selects the friendly mode.
* 1: ''case-insensitive string compare for equality''
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Here are two examples using the date field, the first one outputs the date value in raw format, the second in the friendly format:
* 2: ''numeric compare for equality''
 
* 3: ''numeric less than''
 
* 4: ''numeric less than or equal to''
 
* 5: ''numeric greater than''
 
* 6: ''numeric greater than or equal to''
 
* 7: ''substring search (case sensitive)''
 
* 8: ''substring search (case insensitive)''
 
  
'''In all cases, the first value is always compared with the second value, never the other way around'''
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<div style="margin-left: 20pt"><span style="font-family: monospace,monospace; font-size:1em;">field(date, 0)</span></div>
|- valign="top"
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<div style="margin-left: 20pt"><span style="font-family: monospace,monospace; font-size:1em;">field(date, 1)</span></div>
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Examples
 
|style="background: #ecfeea; color: black; border: 1px solid black" | '''isequal([artist],[album],1)'''<br>''If the 'artist' and 'album' values are the same, the output will be 1, otherwise, the output will be 0.''
 
  
<br>'''if(isequal([artist],[album],1),Self Titled,[album])'''
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==== Field Values: Empty, 0, and 1 ====
<br>''Wrapped inside an 'If' function, if the 'artist' and 'album' values are the same, the output will be 'Self Titled', otherwise, the output will be the 'album' value.''
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The Media Center expression language does not strongly differentiate between the numeric value zero <span style="font-family: monospace,monospace; font-size:1em;">0</span> and emptiness
 +
for numeric field types Integer and Decimal.
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And in some cases, the numeric value of <span style="font-family: monospace,monospace; font-size:1em;">1</span> is treated similarly to the empty value.
  
<br>'''if(isequal([artist],[album],1),Self Titled/,,[album]/))'''
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When a value of 0 is entered as a numeric field's value, the raw value will be shown as <span style="font-family: monospace,monospace; font-size:1em;">0</span>,
<br>''This example demonstrates the character 'escaping' mentioned in the [[#Overview|overview]] earlier. Here, we want the output to be either "Self Titled," (note the inclusion of the comma) or the album value with a closing parenthesis. In order to achieve this, the comma, and the closing parenthesis, are escaped using a preceding forward-slash character. This informs the expression evaluator that these characters are not part of the expression syntax and are to be treated literally''
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but the display format (as in the file list) will be shown as empty.
 +
The empty display allows for less visual noise in the user interface, since a column full of <span style="font-family: monospace,monospace; font-size:1em;">0</span> values is not usually helpful.
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In fact, if you attempt to set a numeric field's value to <span style="font-family: monospace,monospace; font-size:1em;">0</span> in the file list, it will immediately be displayed as empty.
  
<br>'''if(isequal([filename (path)],Classical,8),Classical,Not Classical)'''
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Generally this difference is unimportant, except when testing numeric values with [[Test_and_Comparison_Functions#IsEmpty|IsEmpty()]] or [[Test_and_Comparison_Functions#IsEqual|IsEqual()]].
<br>''Here, compare mode number eight has been specified, so, if the letters classical appear anywhere in the file path for a given file, the expression will return "Classical" and if not, it will return "Not&nbsp;Classical".'' '''Note that when using compare modes seven and eight, the subject must be given first, and the term to compare for given second'''
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It is easy to be fooled when testing such a value if the value shown in a file list is empty.
|}
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The values shown in the Tag Action Window will reveal the actual raw value, as will an expression column using the field's raw format.
<div style="text-align:right;">([[#top|Back to top)]]</div>
 
  
====IsEmpty(...): Tests to see if a field is empty====
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Another consideration for integer fields is that when sorting, a <span style="font-family: monospace,monospace; font-size:1em;">1</span> value can sometimes sort indistinguishably from an empty value.
{| style="width: 100%; border: 1px solid black" align="top" border="1" cellpadding="3"
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The Integer type <span style="font-family: monospace,monospace; font-size:1em;">disc #</span> field is typically empty when an album consists of only one disc, and as such, Media Center will sort
|- valign="top"
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the <span style="font-family: monospace,monospace; font-size:1em;">disc #</span> values of empty (<span style="font-family: monospace,monospace; font-size:1em;">0</span>) and <span style="font-family: monospace,monospace; font-size:1em;">1</span> identically.
! scope="row" style="white-space:nowrap; background: #A8E4A0; color: black; border: 1px solid black;" width=100 | IsEmpty()
 
| style="background: #ecfeea; color: black; border: 1px solid black" width=1200 | Tests any given field for data. If the field is empty, the function returns 1, and if populated, the function returns 0. There are two different test modes available, a "string" test, and a "number" test. This is because as far as MEDIA CENTER is concerned, fields designated as containing numerical values that are populated with the number zero, are empty. If no test mode is specified, the function will default to 0.
 
Pay particular attention to the third example offered below, as it covers a caveat that comes with this particular function.
 
|- valign="top"
 
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Construction
 
| style="background: #ecfeea; color: black; border: 1px solid black" | '''isempty([field to test],test mode)'''
 
''Available test modes:''
 
* 0: ''String test (field must be empty to get a positive result)''
 
* 1: ''Numerical test (field must be empty, or contain 0 to get a positive result)''
 
|- valign="top"
 
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Examples
 
|style="background: #ecfeea; color: black; border: 1px solid black" | '''isempty([comment],0)'''<br>''If the comment field is empty, this expression will return 1, but if the comment field contains data, the expression will return 0.''
 
  
<br>'''isempty([track #],1)'''
+
The friendly output of a field can differ, depending on context.
<br>''This expression will perform a numerical test for data in the [track #] field. If the field is empty, or contains 0, the expression will return a positive result, 1, otherwise, the result will be negative, 0.''
+
For example, in a file list, and empty field will be shown as blank, but in the Rename, Move & Copy tool,
 +
it will be output as <span style="font-family: monospace,monospace; font-size:1em;">Unknown Disc #</span> (this ensures no blank values are generated as path components).
 +
To test such a field, always use and test against the raw format, and then expressions will be context agnostic.
  
<br>'''if(isempty([disc #]),,[disc #])'''
+
===Field Assignment===
<br>''Here, by not entering any instructions to carry out for a positive result, the expression will do just that, and output nothing, but if the [disc #] field does contain data, the expression will write that out. Upon first look, you would think that this could work really well in the "Rename, Move and Copy Files" tool for only creating a \Disc #\ directory if needed. This will not work. When asking the rename tool to create directories from field data, it is smart enough to know that directories with no name are illegal in Windows, so when it encounters an empty field, it automatically converts it to "Unknown&nbsp;[Field&nbsp;Name]". It does this before the expression engine gets to see it, which means that the IsEmpty function will always return a negative result when used in the rename tool, even when the specified field is indeed empty. As we now know that empty fields are passed through the rename tool as "Unknown&nbsp;[field&nbsp;name]" we can use '''if([[#IsEqual(...): Compares two values in one of nine specified modes|isequal]]([disc&nbsp;#],unknown,8),,[disc&nbsp;#])''' to achieve the desired result. Note that this only applies when using the rename files tool.''
+
<div>
|}
+
The output of an expression can be used to assign a value to a tag.
<div style="text-align:right;">([[#top|Back to top)]]</div>
+
This is accomplished by preceding the expression with an <span style="font-family: monospace,monospace; font-size:1em;">=</span> character.
====IsRange(...): Tests a value for inclusion within a given range====
+
The <span style="font-family: monospace,monospace; font-size:1em;">=</span> character causes the tagging engine to invoke the expression evaluator first,
{| style="width: 100%; border: 1px solid black" align="top" border="1" cellpadding="3"
+
and then to use its output as the value to assign to the field.
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+
[[File:Field_Assignment_with_Expression.png|right]]
! scope="row" style="white-space:nowrap; background: #A8E4A0; color: black; border: 1px solid black;" width=100 | IsRange()
+
Without the prepended <span style="font-family: monospace,monospace; font-size:1em;">=</span> character, the literal expression text itself and not its evaluated value would be stored in the tag.
| style="background: #ecfeea; color: black; border: 1px solid black" width=1200 | IsRange allows us to test if any given field falls inside any given range of values. If the field falls inside the given range, the function returns 1, and if outside the given range, the function returns 0.
+
The expression can refer to the field's own value to modify itself, and this offers a convenient way to perform complex transformations on field values.
|- valign="top"
+
For example, the assignment expression
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Construction
 
| style="background: #ecfeea; color: black; border: 1px solid black" | '''IsRange([Field to Test],Specified-Range)'''
 
''The range to test for can be letters or numbers, separated by a hyphen, without spaces, lowest value first, highest second. Letters and numbers cannot be mixed, the range can only be one or the other''
 
* ''1-100''
 
* ''a-z''
 
* ''c-d''
 
* ''23-7542''
 
|- valign="top"
 
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Examples
 
|style="background: #ecfeea; color: black; border: 1px solid black" | '''isrange([artist],a-c)'''<br>''Abba or Blondie will return 1 (positive), and ZZ Top will return 0 (negative).''
 
  
<br>'''if(isrange([bitrate],96-191),Poor Quality,High Quality)'''
+
<div style="margin-left: 20pt"><span style="font-family: monospace,monospace; font-size:1em;">=removeleft([name], 4)</span></div>
<br>''This expression will output "Poor Quality" for any file where the bitrate falls between 96 and 191, and "High Quality" for all others. Note that expressions are only as good as the instructions given, and that the above expression would label files with bitrates less than 96kbps as "High Quality". If this expression were used to add a category to a view, there would be two selectable choices in the category, Low Quality, and High Quality. Selecting either one would then filter the file list accordingly.''
 
  
<br>'''[http://yabb.jriver.com/interact/index.php?topic=38566.msg262229#msg262229 This post]''' ''on Interact shows the use of IsRange in a Search List. (right click the link, open in new tab to keep this page open). The expression format in that post shows how to form expressions for use in standard MEDIA CENTER searches, something that was covered earlier'' [[#When, Where and How to use expressions|on this page.]]
+
entered into an edit cell for the <span style="font-family: monospace,monospace; font-size:1em;">name</span> field would remove
|}
+
four characters from the left of the <span style="font-family: monospace,monospace; font-size:1em;">name</span> field's current value.
<div style="text-align:right;">([[#top|Back to top)]]</div>
+
An assignment expression can be entered into the Tag Action Window, or by using inline editing in the file list or a pane entry.
====IsMissing(...): Tests to see if a file exists on the system====
+
The image on the right shows in-place field assignment.
{| style="width: 100%; border: 1px solid black" align="top" border="1" cellpadding="3"
 
|- valign="top"
 
! scope="row" style="white-space:nowrap; background: #A8E4A0; color: black; border: 1px solid black;" width=100 | IsMissing()
 
| style="background: #ecfeea; color: black; border: 1px solid black" width=1200 | This function checks to see if a file exists on the system. If the file is missing, the function returns 1 (positive), and if the file is found, the function returns 0 (negative). It is possible to specify a specific file to check for, but if you know that much, it will be quicker to fire up explorer and check yourself. This function comes in handy for checking the integrity of your MEDIA CENTER library as you can use it to produce a list of any files in your library that MEDIA CENTER cannot find. However, be aware that the larger your library, the longer this list will take to produce as MEDIA CENTER will need to physically check each files' existance in turn.
 
|- valign="top"
 
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Construction
 
| style="background: #ecfeea; color: black; border: 1px solid black" | '''IsMissing(Full Path To File)'''
 
''If no file path is specified, the function will default to checking the current file.''
 
|- valign="top"
 
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Examples
 
|style="background: #ecfeea; color: black; border: 1px solid black" | '''ismissing()'''<br>''Checks if the current file exists, and returns 1 (positive) if the file does not exist, and 0 (negative) if the file does exist.''
 
  
<br>'''ismissing(C:\Music\My Lost File.mp3)'''
+
Note: Undo is supported, reverting each tag to its value prior to the assignment.
<br>''Checks for "My Lost File.mp3" and returns 1 (positive) if the file does not exist, and 0 (negative) if the file does exist.''
+
Redo is also supported, reapplying the most recent Undo.
 +
</div>
  
<br>'''[=ismissing([filename])]=1'''
+
== Expression Language Syntax ==
<br>''This example also demonstrates how to construct an expression for use as a MEDIA CENTER search string. If you place this in the search field in the top right corner of the program while viewing all of your library, it will filter the list, leaving only the missing files on view. If your library is in good order, this list should be empty. You could also create a view scheme and use this string in the "Set rules for file display" search to give you a view that you can visit periodically to check that your library is intact
+
Now that the basics have been covered, the more rigorous rules of the expression language syntax can be described.
  
<br>'''if(ismissing(),File is missing,File exists)'''
+
:* An expression is any sequence of literal text and any number of function calls.
<br>''Wrapped inside an "If()" function, the expression outputs "File is missing" or "File Exists" depending on the result returned by IsMissing()''
+
:* Expressions are read and evaluated left to right. Literal text is output unmodified, function calls are evaluated and their return values output.
|}
+
:* Fields designated using [[square bracket notation]] are expanded into the equivalent [[Accessing_and_Storing_Functions#Field|Field()]] function call.
<div style="text-align:right;">([[#top|Back to top)]]</div>
+
:* Nested function calls are evaluated from the innermost function to outermost function, and again, left to right when one function follows another.
====IsRemovable(...): Tests to see if a file is stored on removable media====
+
:* A function is evaluated and its returned value contextually replaces the function call in the expression
{| style="width: 100%; border: 1px solid black" align="top" border="1" cellpadding="3"
+
:* Within a function's argument list, whitespace is ignored before and after commas, after an opening parenthesis, and before a closing parenthesis.
|- valign="top"
+
:* The forward-slash escape character <span style="font-family: monospace,monospace; font-size:1em;">/</span> disables the special meaning of the character that follows it.
! scope="row" style="white-space:nowrap; background: #A8E4A0; color: black; border: 1px solid black;" width=100 | IsRemovable()
+
:* The escape sequence <span style="font-family: monospace,monospace; font-size:1em;">/#</span> followed by <span style="font-family: monospace,monospace; font-size:1em;">#/</span> escapes everything inside.
| style="background: #ecfeea; color: black; border: 1px solid black" width=1200 | Checks to see if a file resides on removable media and if so, returns 1 (positive), and if not, returns 0 (negative). There is not a lot to say about this function, especially since MEDIA CENTER comes equipped with a [Removable] field by default that is automatically populated with 1 for all files in the library that are on removable storage. The function works in exactly the same way as the IsMissing function described above, returning 1 (positive) if the file is on removable storage, and 0 (negative) if not.
+
:* To use a literal parenthesis, comma, or whitespace inside of function argument lists, escape them. Whitespace within an argument's value is literal and does not need to be escaped when it is surrounded by other non-whitespace text.
|- valign="top"
+
:* An expression may be split into multiple lines, but when it does not satisfy the conditions above regarding whitespace around function parenthesis and commas, use a forward-slash escape as the last character before the newline. Extraneous newlines in the expression editor will produce a trailing ellipsis (...) in the output.
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Construction
 
| style="background: #ecfeea; color: black; border: 1px solid black" | '''IsRemovable(Full Path To File)'''
 
  
''If no file path is specified, the function will default to checking the current file.''
+
=== How Expressions Are Evaluated ===
|- valign="top"
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Expressions are evaluated in the context where they are used.
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Examples
+
For example, an expression column in a file list is evaluated relative to those files in the file list.
|style="background: #ecfeea; color: black; border: 1px solid black" | '''isremovable()'''<br>''Checks if the current file is on removable storage, and if so, returns 1 (positive), if not, the function returns 0 (negative).''
+
And the general flow is that for each file in the list, the expression is evaluated and produces output.
|}
+
The expression only has access to the fields available for the file currently being evaluated.
<div style="text-align:right;">([[#top|Back to top)]]</div>
+
This is important to remember, so it bears repeating.
====IsInPlayingNow & IsPlaying(...): Tests to see if a file is in the Playing Now playlist or currently being played====
+
One file after another, an expression is evaluated against that single file, its output is produced and stored away for use later,
{| style="width: 100%; border: 1px solid black" align="top" border="1" cellpadding="3"
+
and then the result of that evaluation is entirely forgotten before the next file is evaluated.
|- valign="top"
+
This means, the expression evaluator cannot use the results from one file's evaluated expression with the results of another
! scope="row" style="white-space:nowrap; background: #A8E4A0; color: black; border: 1px solid black;" width=100 | IsInPlayingNow()
+
file's evaluation.
| rowspan="2" style="background: #ecfeea; color: black; border: 1px solid black" width=1200 | These two functions will be dealt with together as from their names, they are self-explanatory. One checks to see if a file has been added to the playing now list in any zone, and the other checks if a file in a list is currently playing or not, in any zone. With this in mind, their most practical use is as expression columns in a file list. To add an expression column to a list, right click on any existing column header and click on the "Add expression column" option.
 
|- valign="top"
 
! scope="row" style="white-space:nowrap; background: #A8E4A0; color: black; border: 1px solid black;" width=100 | IsPlaying()
 
|- valign="top"
 
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Construction
 
| style="background: #ecfeea; color: black; border: 1px solid black" | '''IsInPlayingNow()'''<br>''Checks the current file, and if in the Playing Now list, returns 1 (positive), and if not, returns 0 (negative).
 
  
<br>'''IsPlaying()'''
+
=== Expressions and Locales ===
<br>''Checks the current file, and if currently playing, returns 1 (positive), and if not, returns 0 (negative).
+
Media Center will respect the Windows locale setting for output values produced by certain functions,
|- valign="top"
+
and within the values of certain fields.
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Examples
+
This is important to consider when writing expressions that consume such values.
|style="background: #ecfeea; color: black; border: 1px solid black" | '''if(isinplayingnow(),Selected,Not Selected)'''<br>''As mentioned in the description, the ideal place for these functions is as 'expression columns'. If this example were used in an expression column, then files added to Playing Now will show as "Selected" and all other files would show as "Not Selected". If the idea here is to be able to quickly see which files have been added, this might look a bit 'busy' and defeat the purpose, to which end, it is perfectly acceptable to tell the expression that if a file is not in Playing Now, to output nothing, by simply not giving any instructions for the negative result, like so: '''if(isinplayingnow(),Selected,)'''. Now, this expression column will only show "Selected" against files that are in Playing Now, leaving all others empty, giving a much easier column to read.
+
Under most circumstances, such values cause no harm.
 +
However special care must be taken with functions that require the use of period as the decimal point.
 +
One such function is [[Miscellaneous_Functions#Math|Math()]], which always uses period as the decimal point.
 +
If your locale uses some other character such as comma, these characters will have to be converted into periods before the
 +
critical function is called.
 +
Handling this problem is not difficult. Before passing to [[Miscellaneous_Functions#Math|Math()]] any floating point number,
 +
use [[String_Manipulation_Functions#Replace|Replace()]] first when necessary to convert the locale's decimal character into a period.
 +
Fields that cause problems are any fields that produce floating-point values,
 +
such as any Date type field in raw format (e.g. <span style="font-family: monospace,monospace; font-size:1em;">[date,0]</span>, <span style="font-family: monospace,monospace; font-size:1em;">[last played,0]</span>, <span style="font-family: monospace,monospace; font-size:1em;">[date modified,0]</span>, and <span style="font-family: monospace,monospace; font-size:1em;">[date imported,0]</span>),
 +
or any textual field that contains floating-point values that will be used for various calculations
 +
(e.g. any of the Dynamic Range variants).
 +
Certain functions such as [[Date_and_Time_Functions#Now|Now()]] and [[Date_and_Time_Functions#ConvertTime|ConvertTime()]] also return localized floating-point values.
 +
Consider also that the expression parser uses comma as the argument separator.
 +
Any literal numeric values specified as a function argument must have any embedded commas escaped.
  
<br>Use'' IsPlaying ''in exactly the same way as IsInPlayingNow()''
+
=== A Complex Expression Example ===
 +
[[File:Expression_Editor.png|right]]
 +
Here is a more complex expression example that illustrates the various rules discussed above regarding expressions:
  
<br>''On the Interact support forum,'' '''[http://yabb.jriver.com/interact/index.php?topic=57461.0 mark_h describes how he puts these two functions to work for him]''', ''and rick.ca shows how he tweaked the idea when he answers the question:'' '''"[http://yabb.jriver.com/interact/index.php?topic=58137.msg393905#msg393905 is it possible to play an artist's full work when a genre is shuffling?]"'''
+
<span style="font-family: monospace,monospace; font-size:1em;">
|}
+
<div style="margin-left: 20pt">if(  IsEmpty( [Disc #),</div>
<div style="text-align:right;">([[#top|Back to top)]]</div>
+
<div style="margin-left: 40pt">Disc number is empty,</div>
<br><br>
+
<div style="margin-left: 40pt">Delimit(</div>
===Change how existing data is displayed using Format functions===
+
<div style="margin-left: 60pt">field(disc #) , </div>
All of these functions (with the exception of FormatBoolean) take raw data from the library and allow us to present that data in a way that we choose. What does "raw data" mean? MEDIA CENTER stores duration information in seconds and converts that information into hours (if needed), minutes and seconds for display in the Duration column in a file list. Likewise, file size information is stored in bytes and is converted into Mb for display in the file list. Dates are stored using a UNIX system (use google if you want to know more about that) which means that the date field could contain 40121.8272916666683159 and MEDIA CENTER will display that as 04/11/2009 19:51 (if that is how your Windows locale setting displays date and time). So there you have it, raw data. The following section gives some idea of what is possible using the raw data and the Format functions. '''''To&nbsp;instruct the expression evaluator to use raw data, a zero is added to the library field, inside the square brackets, like so: [Date Imported,0]'''''
+
<div style="margin-left: 60pt">/)    ,</div>
====FormatDate(...): Formats a date value in a specified manner====
+
<div style="margin-left: 60pt">DISC /(</div>
{| style="width: 100%; border: 1px solid black" align="top" border="1" cellpadding="3"
+
<div style="margin-left: 40pt">)</div>
|- valign="top"
+
<div style="margin-left: 20pt">)</div>
! scope="row" style="white-space:nowrap; background: #A8E4A0; color: black; border: 1px solid black;" width=100 | FormatDate()
+
</span>
| style="background: #ecfeea; color: black; border: 1px solid black" width=1200 | As mentioned in the [[#Change how existing data is displayed using Format functions|section introduction above]], MEDIA CENTER stores date information in a UNIX style, and converts that information into legible date/time information we can understand. By default, MEDIA CENTER presents dates using the system locale settings. This function can be applied to any default library field that contains date information in order to have that information displayed in a non-default format.
 
|- valign="top"
 
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Construction
 
| style="background: #ecfeea; color: black; border: 1px solid black" | '''formatdate([date field,0],Format,Output if date is empty)'''
 
  
''Available format choices:''
+
The expression demonstrates that
 +
:* whitespace before and after commas or opening and closing parenthesis is ignored
 +
:* expressions can be safely split into multiple lines using the whitespace rules just mentioned
 +
:* function and field names are case insensitive
 +
:* forward slash is used and required to escape parenthesis (see inside the [[Formatting_Functions#Delimit|Delimit()]] function)
 +
:* whitespace does not require escapement when surrounded by other characters (see after the <span style="font-family: monospace,monospace; font-size:1em;">C</span> in <span style="font-family: monospace,monospace; font-size:1em;">DISC</span>)
 +
:* literal text is output unmodified (<span style="font-family: monospace,monospace; font-size:1em;">Disc number is empty</span>)
 +
:* functions can be nested (Both [[Test_and_Comparison_Functions#IsEmpty|IsEmpty()]] and [[Formatting_Functions#Delimit|Delimit()]] are nested within the [[Conditional_Functions#If|If()]] function, and the [[Accessing_and_Storing_Functions#Field|Field()]] function is nested within [[Formatting_Functions#Delimit|Delimit()]]
  
* Year ''Returns the full year, i.e. 2010''
+
When the expression is run, files that have no disc number will produce <span style="font-family: monospace,monospace; font-size:1em;">Disc number is empty</span>,
* Month ''Returns the full month, i.e. April, November.''
+
and files that have, say, a disc number value of <span style="font-family: monospace,monospace; font-size:1em;">3</span> will produce <span style="font-family: monospace,monospace; font-size:1em;">DISC (3)</span>.
* Day ''Returns the day in number format, i.e. 23 (note that single numbers have no leading zero)''
 
* Filename ''Returns a filename friendly date format that also includes the seconds&nbsp;information to help avoid file names clashing, i.e. 20040521-032221''
 
* Elapsed ''Returns "how long ago" information, i.e. 2.43 Days or 1.85 Years''
 
* Date ''Returns the date using the system format on the machine running the expression.''
 
* DateTime ''Returns the date and time using the system format on the machine running the expression.''
 
* hour ''Returns the hour from dates with time information. (note that single numbers have no leading zero)''
 
* minute ''Returns minutes from dates with time information. (note that single numbers have no leading zero)''
 
  
''Flexible formatting is also available: ('''Note that these <ins>are case sensitive</ins>)'''''
+
== Functions ==
  
* yy ''Returns the last two digits of the year''
+
Functions enable you to transform or generate content automatically. For background information on how functions are used in expressions, refer to [[#The Anatomy of an Expression|The Anatomy of an Expression]] section above.
* yyyy ''Returns the full year''
 
* MM ''Returns the month as two digits''
 
* MMM ''Returns the month as three letter abbreviations''
 
* MMMM ''Returns the month in full''
 
* dd ''Returns the day as two digits''
 
* ddd ''Returns the day as three letter abbreviations''
 
* dddd ''Returns the full day''
 
  
Output if date is empty: ''If the date is empty, anything placed here will be output instead. This could be plain text, such as "No Date", or a library field. This value is optional, and if not given, the expression will default to return nothing if the date is empty.''
+
This section describes all the various functions provided by Media Center's Expression Language.
|- valign="top"
 
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Examples
 
|style="background: #ecfeea; color: black; border: 1px solid black" | '''formatdate([last played,0],yyyy//MM//dd,Not Yet)'''<br>''This will return the last played date as year/month/day without the time, and regardless of the system locale setting. If a file has no last played info, the expression will output "Not&nbsp;Yet" instead.''
 
  
<br>'''formatdate([date imported,0],month)'''
+
=== Function Arguments ===
<br>''This will return the month a file was imported, written in full. For example, December, as opposed to 12.
 
  
<br>'''formatdate([date imported,0],month)&datatype=[month]'''
+
As discussed [[#The_Anatomy_of_an_Expression|above]], a function call consists of the function's case-insensitive name, immediately followed by an opening parenthesis character, one or more comma-separated arguments, and a closing parenthesis character:
<br>''If you were to use the previous expression to create a view category that contained the months your files were imported, it would list the months alphabetically, with April first and September last. Thankfully, we can specify "data types" for expressions which further fine tune how MEDIA CENTER displays the results. In this case, a data type of month has been specified, therefore MEDIA CENTER will list the months in the correct chronological order. Data types were discussed [[#Specify data types for expression based fields|earlier on this page]].
 
|}
 
<div style="text-align:right;">([[#top|Back to top)]]</div>
 
====FormatNumber(...): Formats a number to a specified number of decimal places====
 
{| style="width: 100%; border: 1px solid black" align="top" border="1" cellpadding="3"
 
|- valign="top"
 
! scope="row" style="white-space:nowrap; background: #A8E4A0; color: black; border: 1px solid black;" width=100 | FormatNumber()
 
| style="background: #ecfeea; color: black; border: 1px solid black" width=1200 | '''FormatNumber()''' allows to format any given value to a set number of decimal places.
 
|- valign="top"
 
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Construction
 
| style="background: #ecfeea; color: black; border: 1px solid black" | '''FormatNumber(Value to format,Number of decimal places,Output if value is zero,Label if value is greater than 1,Label if value equals 1)'''
 
  
* "Value to format" ''This could be a library field, such as [replay gain] or the result of a [[#Math(...): Evaluates a given mathematical formula|Math()]] expression. Any numerical value you encounter where you would like to limit the number of decimal places displayed can have this function applied.''
+
<div style="margin-left: 20pt"><span style="font-family: monospace,monospace; font-size:1em;"><i>functionname</i><b>(</b><i>argument 1</i>, <i>argument 2</i>, ...<b>)</b></span></div>
* "Number of decimal places" ''This is optional. If not specified, the function will default to zero decimal places. Use -1 to output as many decimal places as necessary.''
 
* "Output if value is zero" ''This is optional. If not specified, the function will return zero.''
 
* "Label if value is greater than 1" ''This is optional. If not specified, the function will not return anything, if specified, and the formatted number is greater than 1, the function will return with the number, plus this label.''
 
* "Label if value equals 1" ''This is optional, as detailed below..''
 
** If not specified, but a label for greater than 1 has been specified, then this "greater than 1" label will always be used.
 
** If neither are specified, the function will not return anything.
 
** If both are specified, and the formatted number equals 1, the function will return with the number, plus this label.''
 
  
''Note that even if you are only interested in applying a label for those results that equal 1, you must also indicate the preceding instructions, if only to instruct the evaluator to ignore them, as shown in the examples below.''
+
Functions may have one or more arguments. In some cases, these arguments are optional, and will automatically use a default value if omitted. For example, these two expressions are equivalent because the mode argument for [[Test_and_Comparison_Functions#IsEmpty|IsEmpty()]] is optional and defaults to 0:
|- valign="top"
+
:<span style="font-family: monospace,monospace; font-size:1em;">isempty([comment], 0)</span>
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Examples
+
:<span style="font-family: monospace,monospace; font-size:1em;">isempty([comment])</span>
|style="background: #ecfeea; color: black; border: 1px solid black" | '''formatnumber([duration,0],2)'''<br>''This will return the duration of a track, in seconds, shown to two decimal places.''
 
  
<br>'''formatnumber([number plays,0],0,Not played this one yet,Plays,Play)'''
+
In this case, a comma-separator will still be required if additional arguments follow the optional one. Whitespace after the commas is also optional, but helps readability and formatting. However, if any extra arguments are included in a function call which are not valid for that function, they are dropped and omitted from output. This is of particular importance when using string-manipulation functions on text. If the text you enter contains any commas, these must be escaped or the expression engine will consider text after the comma to be additional arguments.
* "0" decimal places has been specified, therefore the result will be a whole number with no decimals shown.
 
* ''If [number plays] is zero, the result will be "Not played this one yet"''
 
* ''If [number plays] is greater than 1, lets say 6, the result will be "6 Plays"''
 
* ''If [number plays] is 1, the result will be "1 Play"''
 
  
<br>'''formatnumber([number plays,0],,,,Time)'''
+
The arguments themselves are also just expressions, and you can nest multiple functions to achieve complex logic:
''Here, the function will fall back to its defaults for everything except when the number equals one:''
+
:<span style="font-family: monospace,monospace; font-size:1em;">if(isequal([artist], [album], 1), Eponymous, [album])</span>
* ''No decimal places have been specified, the result will default to a whole number with no decimals shown.''
 
* ''If [number plays] is zero, the result will be "0"''
 
* ''If [number plays] is greater than 1, lets say 6, the result will be "6"''
 
* ''If [number plays] is 1, the result will be "1 Time"''
 
|}
 
<div style="text-align:right;">([[#top|Back to top)]]</div>
 
====PadNumber(...): Adds leading zeros to any given number====
 
{| style="width: 100%; border: 1px solid black" align="top" border="1" cellpadding="3"
 
|- valign="top"
 
! scope="row" style="white-space:nowrap; background: #A8E4A0; color: black; border: 1px solid black;" width=100 | PadNumber()
 
| style="background: #ecfeea; color: black; border: 1px solid black" width=1200 | This function is not a 'Format' function by name, but is by nature, hence its inclusion in this section. PadNumber is a nice, simple function that is used to add leading zeros to any given number value.
 
|- valign="top"
 
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Construction
 
| style="background: #ecfeea; color: black; border: 1px solid black" | '''PadNumber(Field to pad,Total number of digits required)'''
 
|- valign="top"
 
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Examples
 
|style="background: #ecfeea; color: black; border: 1px solid black" | '''padnumber([track #],2)'''<br>''This will add a leading zero to all track numbers between one and nine.''
 
  
<br>'''padnumber([[#Counter(...): Counts upwards in specified increments|counter()]],4)'''
+
Nested function calls are always treated as a ''single'' argument when used as the input to another function (so that commas in the output of one function do not need to be escaped to be used as input in another function). This includes fields, since they are expanded to the equivalent [[Accessing_and_Storing_Functions#Field|Field()]] function call.
<br>''here, the output from the counter() function will be 'padded' to 4 characters: 0001, 0002, 0003, etc. etc.''
 
|}
 
<div style="text-align:right;">([[#top|Back to top)]]</div>
 
====FormatDuration(...): Presents a duration of seconds in a reader friendly format====
 
{| style="width: 100%; border: 1px solid black" align="top" border="1" cellpadding="3"
 
|- valign="top"
 
! scope="row" style="white-space:nowrap; background: #A8E4A0; color: black; border: 1px solid black;" width=100 | FormatDuration()
 
| style="background: #ecfeea; color: black; border: 1px solid black" width=1200 | MEDIA CENTER stores duration data in seconds, at up to sixteen decimal places. The value shown in the default "Duration" column in a file list is an internally formatted interpretation of this raw "Duration" data. As MEDIA CENTER automatically applies this formatting for us, there is not a lot of call for this particular function.
 
|- valign="top"
 
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Construction
 
| style="background: #ecfeea; color: black; border: 1px solid black" | '''FormatDuration(Value to format)'''
 
  
''"Value to format" can be either the raw duration data, or a given number of seconds''
+
:'''''Please Note:''''' In some cases below, such as with [[String_Manipulation_Functions#Unswap|Unswap()]], we have ignored this detail in order to simplify the examples. If you enter any text manually into a function, all commas ''must be'' escaped in order to achieve the correct result. This detail is unimportant in most real-world usages, however, because you will typically use either field values or the output of other functions as the arguments in your expressions. However, if you need to include commas in a string literal argument to a function, you need to escape every one, or block escape the entire argument.
|- valign="top"
 
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Examples
 
|style="background: #ecfeea; color: black; border: 1px solid black" | '''formatduration([duration,0])'''<br>''This expression will duplicate the contents of the default [duration] field as shown in a file list''
 
  
<br>'''formatduration(600)'''
+
=== [[Function Index]] ===
<br>''This will output ten minutes in the format 10:00''
 
|}
 
<div style="text-align:right;">([[#top|Back to top)]]</div>
 
====FormatFileSize(...): Presents a number of bytes in a reader friendly format====
 
{| style="width: 100%; border: 1px solid black" align="top" border="1" cellpadding="3"
 
|- valign="top"
 
! scope="row" style="white-space:nowrap; background: #A8E4A0; color: black; border: 1px solid black;" width=100 | FormatFilesize()
 
| style="background: #ecfeea; color: black; border: 1px solid black" width=1200 | MEDIA CENTER stores file size data internally in bytes. This function will convert those byte values into reader-friendly values, 3.2 Kb or 10.4 Mb, for example. The function will also accept a byte value directly.
 
|- valign="top"
 
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Construction
 
| style="background: #ecfeea; color: black; border: 1px solid black" | '''FormatFileSize(Value to format)'''
 
  
''"Value to format" can be either the raw [File Size] data or a given number of bytes.
+
==== [[Accessing and Storing Functions]] ====
|- valign="top"
+
* '''[[Accessing_and_Storing_Functions#Field|Field(&hellip;)]]''': Returns a field's value.
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Examples
+
* '''[[Accessing_and_Storing_Functions#Load|Load(&hellip;)]]''': Outputs the value of a [[global variable]].
|style="background: #ecfeea; color: black; border: 1px solid black" | '''formatfilesize([file size,0])'''<br>''This expression will duplicate the contents of the default [file size] field as shown in a file list''
+
* '''[[Accessing_and_Storing_Functions#Note|Note(&hellip;)]]''': Retrieve note fields.
 +
* '''[[Accessing_and_Storing_Functions#Save|Save(&hellip;)]]''': Saves a value to a [[global variable]].
 +
* '''[[Accessing_and_Storing_Functions#SaveAdd|SaveAdd(&hellip;)]]''': Adds to a [[global variable]].
 +
* '''[[Accessing_and_Storing_Functions#Tag|Tag(&hellip;)]]''': Returns a file's physical tag.
  
<br>'''formatfilesize(56123456)'''
+
==== [[Conditional Functions]] ====
<br>''This expression will convert 56,123,456 bytes and the output will be 53.5 MB''
+
* '''[[Conditional Functions#If|If(&hellip;)]]''': Conditional ifelse evaluator.
|}
+
* '''[[Conditional Functions#IfElse|IfElse(&hellip;)]]''': Conditional if-elseif evaluator.
<div style="text-align:right;">([[#top|Back to top)]]</div>
+
* '''[[Conditional Functions#FirstNotEmpty|FirstNotEmpty(&hellip;)]]''': Returns the first non-empty argument.
====FormatRange(...): Formats a value as a range====
 
{| style="width: 100%; border: 1px solid black" align="top" border="1" cellpadding="3"
 
|- valign="top"
 
! scope="row" style="white-space:nowrap; background: #A8E4A0; color: black; border: 1px solid black;" width=100 | FormatRange()
 
| style="background: #ecfeea; color: black; border: 1px solid black" width=1200 | This function places any given value into its place in any given range.
 
|- valign="top"
 
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Construction
 
| style="background: #ecfeea; color: black; border: 1px solid black" | '''FormatRange(Value to format,Range size,Mode)'''
 
'''Value to format:''' ''This could be a specific word or number, or any library field''
 
<br>'''Range Size:''' ''A numerical value dependent on how you wish to set up your range. If not specified, this will default to 1''
 
<br>'''Mode:''' ''There are three possible modes, detailed below. If not specified, this will default to zero.''
 
* '''0:''' ''Automatically choose between number / letter grouping''
 
* '''1:''' ''Specifies that letter grouping should be used''
 
* '''2:''' ''Specifies that number grouping should be used''
 
|- valign="top"
 
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Examples
 
|style="background: #ecfeea; color: black; border: 1px solid black" | '''formatrange([artist])'''<br>''This will return the first letter from the [artist] field. Note that as '''range size''' and '''mode''' values were not specified, the function defaulted to one and automatic respectively.''
 
  
<br>'''formatrange([artist],3,1)'''<br>''This will take the first letter from the artist field and place it in the appropriate letter range. In this case, a range size of three has been specified, therefore the output will be in the form of "a-c", "d-f", "g-i" etc. etc.''
+
==== [[Test and Comparison Functions]] ====
 +
* '''[[Test and Comparison Functions#Compare|Compare(&hellip;)]]''': Compares two numbers.
 +
* '''[[Test and Comparison Functions#IsEqual|IsEqual(&hellip;)]]''': Compares two values in one of nine specified modes
 +
* '''[[Test and Comparison Functions#IsEmpty|IsEmpty(&hellip;)]]''': Tests a value for emptiness
 +
* '''[[Test and Comparison Functions#IsRange|IsRange(&hellip;)]]''': Tests a value for inclusion within a given range
 +
* '''[[Test and Comparison Functions#IsMissing|IsMissing(&hellip;)]]''': Tests to see if a file exists on the system
 +
* '''[[Test and Comparison Functions#IsRemovable|IsRemovable(&hellip;)]]''': Tests to see if a file is stored on removable media
 +
* '''[[Test and Comparison Functions#IsInPlayingNow|IsInPlayingNow(&hellip;)]]''': Tests to see if a file is in the Playing Now playlist
 +
* '''[[Test and Comparison Functions#IsPlaying|IsPlaying(&hellip;)]]''': Tests to see if a file is in currently being played
  
<br>'''formatrange([bitrate],100,2)'''<br>''This will take the bitrate and place it in the appropriate number range. In this case a range of 100 has been specified, therefore the output will be in the form of "0-99", "100-199", "200-299" etc. etc.''
+
==== [[Formatting Functions]] ====
 +
* '''[[Formatting Functions#Delimit|Delimit(&hellip;)]]''': Outputs a value with head/tail strings when value is non-empty
 +
* '''[[Formatting Functions#FormatBoolean|FormatBoolean(&hellip;)]]''': Formats a boolean (true / false) value in a specified manner
 +
* '''[[Formatting Functions#FormatDuration|FormatDuration(&hellip;)]]''': Presents a duration of seconds in a reader friendly format
 +
* '''[[Formatting Functions#FormatFileSize|FormatFileSize(&hellip;)]]''': Presents a number of bytes in a reader friendly format
 +
* '''[[Formatting Functions#FormatNumber|FormatNumber(&hellip;)]]''': Formats and rounds a number to a specified number of decimal places
 +
* '''[[Formatting Functions#FormatRange|FormatRange(&hellip;)]]''': Formats a value as a range
 +
* '''[[Formatting Functions#Orientation|Orientation(&hellip;)]]''': Outputs the orientation of an image
 +
* '''[[Formatting Functions#PadNumber|PadNumber(&hellip;)]]''': Adds leading zeros to any given number
 +
* '''[[Formatting Functions#RatingStars|RatingStars(&hellip;)]]''': Outputs the value of Rating as a number of star characters
 +
* '''[[Formatting Functions#Watched|Watched(&hellip;)]]''': Outputs a formatted video bookmark
  
Note that this function always starts number ranges from zero, 0-9, 10-19, etc, etc.. If you really need a number grouping that starts from 1, 1-10, 11-20, 21-30,etc. etc., you can use expressions to create a pseudo range. Full details, with a helpful explanation, of "1 based grouping" can be found [[CD_Reference_Number|on this page]].
+
==== [[String Manipulation Functions]] ====
|}
+
* '''[[String Manipulation Functions#Clean|Clean(&hellip;)]]''': Clean a string to be used for various operations
<div style="text-align:right;">([[#top|Back to top)]]</div>
+
* '''[[String Manipulation Functions#FixCase|FixCase(&hellip;)]]''': Changes the case of a given string
 +
* '''[[String Manipulation Functions#FixSpacing|FixSpacing(&hellip;)]]''': Intelligently splits adjacent camel-cased words
 +
* '''[[String Manipulation Functions#Hexify|Hexify(&hellip;)]]''': Hexifies a string to make it suitable for web usage
 +
* '''[[String Manipulation Functions#Left|Left(&hellip;)]]''': Retrieves a specified number of characters from the left of a string
 +
* '''[[String Manipulation Functions#Length|Length(&hellip;)]]''': Returns the number of characters in a string
 +
* '''[[String Manipulation Functions#Mid|Mid(&hellip;)]]''': Retrieves specified characters from a string
 +
* '''[[String Manipulation Functions#Regex|Regex(&hellip;)]]''': Regular expression pattern matching and capture
 +
* '''[[String Manipulation Functions#RemoveCharacters|RemoveCharacters(&hellip;)]]''': Removes a list of characters from a string
 +
* '''[[String Manipulation Functions#RemoveLeft|RemoveLeft(&hellip;)]]''': Trims characters from the beginning of a string
 +
* '''[[String Manipulation Functions#RemoveRight|RemoveRight(&hellip;)]]''': Trims characters from the end of a string
 +
* '''[[String Manipulation Functions#Replace|Replace(&hellip;)]]''': Replace or remove a string segment
 +
* '''[[String Manipulation Functions#Right|Right(&hellip;)]]''': Retrieves a specified number of characters from the right of a string
 +
* '''[[String Manipulation Functions#Swap|Swap(&hellip;)]]''': Takes Firstname Lastname and swaps to Lastname, Firstname.
 +
* '''[[String Manipulation Functions#Unswap|Unswap(&hellip;)]]''': Takes Lastname, Firstname and reverses it to Firstname Lastname.
  
====FormatBoolean(...): Formats a boolean (true / false) value in a specified manner====
+
==== [[List Manipulation Functions]] ====
{| style="width: 100%; border: 1px solid black" align="top" border="1" cellpadding="3"
+
* '''[[List Manipulation Functions#ListBuild|ListBuild(&hellip;)]]''': Constructs a list from a series of items
|- valign="top"
+
* '''[[List Manipulation Functions#ListClean|ListClean(&hellip;)]]''': Various list operations
! scope="row" style="white-space:nowrap; background: #A8E4A0; color: black; border: 1px solid black;" width=100 | FormatBoolean()
+
* '''[[List Manipulation Functions#ListCombine|ListCombine(&hellip;)]]''': Combines two delimited lists into a single delimited list
| style="background: #ecfeea; color: black; border: 1px solid black" width=1200 | This function is wrapped around another function and will return specified strings for true and false values returned by that other function.
+
* '''[[List Manipulation Functions#ListCount|ListCount(&hellip;)]]''': Returns the number of items in a list
|- valign="top"
+
* '''[[List Manipulation Functions#ListItem|ListItem(&hellip;)]]''': Returns an item from a location in a list
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Construction
+
* '''[[List Manipulation Functions#ListSort|ListSort(&hellip;)]]''': Sort a list of values
| style="background: #ecfeea; color: black; border: 1px solid black" | '''FormatBoolean(True/False Test,String to use if true,String to use if false)'''
+
* '''[[List Manipulation Functions#ListLimit|ListLimit(&hellip;)]]''': Limits the length of a list
* '''True/False Test''' ''Other functions perform their respective tests and return 1 to indicate a true result, and 0 to indicate a false result''
 
* '''String to use if true,String to use if false''' ''If these are not specified, the function will default to using "True" and "False"''
 
  
|- valign="top"
+
==== [[Date and Time Functions]] ====
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Examples
+
* '''[[Date and Time Functions#ConvertDate|ConvertDate(&hellip;)]]''': Converts a human-readable date to the internal format required for use in date fields
|style="background: #ecfeea; color: black; border: 1px solid black" | '''formatboolean(isempty([number plays]),Never Played,Has Been Played)'''<br>''On it's own, the function'' isempty([number plays]) ''will return either 1 or 0. When wrapped inside a'' formatboolean ''function as shown here, the output for a true result will be "Never Played", and for a false result, the output will be "Has Been Played".
+
* '''[[Date and Time Functions#FormatDate|FormatDate(&hellip;)]]''': Formats a date value in a specified manner
 +
* '''[[Date and Time Functions#Now|Now(&hellip;)]]''': Retrieve and display the system date
  
<br>'''formatboolean(isempty([number plays]))'''<br>''Here, there are no strings specified for the true/false results, therefore the function will default to using "True" and "False"''
+
==== [[File Path and Identifier Functions]] ====
|}
+
* '''[[File Path and Identifier Functions#FileDBLocation|FileDBLocation(&hellip;)]]''': Identifies a file's databases
<div style="text-align:right;">([[#top|Back to top)]]</div>
+
* '''[[File Path and Identifier Functions#FileFolder|FileFolder(&hellip;)]]''': Returns the name of a file's parent
<br><br>
+
* '''[[File Path and Identifier Functions#FileKey|FileKey(&hellip;)]]''': Returns a file's unique internal identifier
===Functions for filename and field manipulation===
+
* '''[[File Path and Identifier Functions#FileName|FileName(&hellip;)]]''': Returns a file's name component
The primary use of the functions in this section is to manipulate the data associated with any given file or files. When used with direct editing in the file list, or in the action window, as decribed [[#When, Where and How to use expressions|here]], they offer extremely fast and efficient methods for batch editing the actual tag data associated with multiple files.<br>Note that when used indirectly, in expression based columns, categories or library fields, the referred fields are not altered in any way, the data is merely presented in the expression field formatted as requested.
+
* '''[[File Path and Identifier Functions#FilePath|FilePath(&hellip;)]]''': Returns a file's path component
====Clean(...): Returns a cleaned up version of a filled in template====
+
* '''[[File Path and Identifier Functions#FileVolume|FileVolume(&hellip;)]]''': Returns a file's volume name component
{| style="width: 100%; border: 1px solid black" align="top" border="1" cellpadding="3"
 
|- valign="top"
 
! scope="row" style="white-space:nowrap; background: #A8E4A0; color: black; border: 1px solid black;" width=100 | Clean()
 
| style="background: #ecfeea; color: black; border: 1px solid black" width=1200 | The official description for this function is simply "Returns a cleaned up version of a filled in template". This function is better explained through demonstration in the examples below.
 
|- valign="top"
 
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Construction
 
| style="background: #ecfeea; color: black; border: 1px solid black" | '''Clean(Template to clean, Mode)'''
 
  
''Template to clean'': a string that will be cleaned
+
==== [[Grouping Functions]] ====
 +
* '''[[Grouping Functions#GroupCount|GroupCount(&hellip;)]]''': Counts the members of a specified group (in a category or field).
 +
* '''[[Grouping Functions#GroupSummary|GroupSummary(&hellip;)]]''': Smartly summarizes the members of a specified group (mode, mean, min, max, etc as is most logical for that grouping).
  
''Mode'' (optional, defaults to 0):
+
==== [[Miscellaneous Functions]] ====
* 0: clean
+
* '''[[Miscellaneous Functions#AlbumArtist|AlbumArtist(&hellip;)]]''': Returns a file's calculated album artist
* 1: remove the article 'The' from the front and tail
+
* '''[[Miscellaneous Functions#AlbumKey|AlbumKey(&hellip;)]]''': Returns a unique album key for a file
* 2: remove all articles (a, an, the, etc.) from the front and tail
+
* '''[[Miscellaneous Functions#AlbumType|AlbumType(&hellip;)]]''': Returns the album type for a file
* 3: replace special characters with -
+
* '''[[Miscellaneous Functions#AudioAnalysisState|AudioAnalysisState(&hellip;)]]''': Returns the state of audio analysis for a file
 +
* '''[[Miscellaneous Functions#Counter|Counter(&hellip;)]]''': Counts upwards in specified increments
 +
* '''[[Miscellaneous Functions#CustomData|CustomData(&hellip;)]]''': Returns internal data to the expression language
 +
* '''[[Miscellaneous Functions#FilePlaylists()|FilePlaylists()]]''': Returns a list of playlists a file belongs to (Can also be used to search)
 +
* '''[[Miscellaneous Functions#Math|Math(&hellip;)]]''': Evaluates a given mathematical formula
 +
* '''[[Miscellaneous Functions#Size|Size(&hellip;)]]''': Returns a file's size in a format specific to the media type
 +
* '''[[Miscellaneous Functions#TrackNumber|TrackNumber(&hellip;)]]''': Returns a file's track # value
 +
* '''[[Miscellaneous Functions#TVInfo|TVInfo(&hellip;)]]''': Miscellaneous television and other pre-formatted information
  
|- valign="top"
+
== Data Types ==
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Examples
+
It was mentioned already that the Media Center expression language is primarily a textual language - it consumes and produces text.
|style="background: #ecfeea; color: black; border: 1px solid black" | '''Clean([Artist] - [Album] /([Genre]/))'''
+
Nonetheless, certain areas of Media Center are influenced by the type of data used or presented,
* First of all, note that this example uses the "forward slash" escaping, as discussed in the [[#Overview|Expressions Overview]] earlier. The result here will be that the [Genre] will be returned wrapped in parenthesis. Without the escaping, the function would fail as the evaluator attempts to read the parenthesis as an integral part of the expression.
+
and sometimes it is useful or necessary to coerce expression output into one data type or another.
 +
Each Media Center field is defined to be of a certain data type,
 +
listed in the [[File_Properties_%28tags%29#Field_Specifications|Field Data Types]] table.
 +
These types influence how values are output, sorted, and interpreted on input.
 +
And expressions always output data of type String.
 +
By coercing the data type of an expression, output formatting and sorting can be controlled in various ways.
  
* Imagine the template without the Clean() function around it. ''[Artist] - [Album] /([Genre]/)''<br>If used as an expression, this string, quite predictably, will return things such as: "AC/DC - Back In Black (Rock)", but, what if one or more of the specified fields contains no data? The result would be rather untidy, such as: "- Back In Black ()" if there were no [artist] or [genre] data.<br>Wrap the template inside the Clean() function to tidy these cases up, so, "- Back In Black ()" would become "Back In Black"
+
Data types are forced by appending to an expression the string:
|}
 
<div style="text-align:right;">([[#top|Back to top)]]</div>
 
  
====FixCase(...): Changes the case of a given string====
+
<div style="margin-left: 20pt"><span style="font-family: monospace,monospace; font-size:1em;">&datatype=[<i>type</i>]</span></div>
{| style="width: 100%; border: 1px solid black" align="top" border="1" cellpadding="3"
 
|- valign="top"
 
! scope="row" style="white-space:nowrap; background: #A8E4A0; color: black; border: 1px solid black;" width=100 | FixCase()
 
| style="background: #ecfeea; color: black; border: 1px solid black" width=1200 | This function will output any given text string in one of five specified case modes.
 
|- valign="top"
 
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Construction
 
| style="background: #ecfeea; color: black; border: 1px solid black" | '''FixCase(String to modify,Case mode to apply)'''<br>''The ''"String to modify"'' can be plain text, a library field, or a combination of the two.''
 
  
The five modes available are:
+
where <i><span style="font-family: monospace,monospace; font-size:1em;">type</span></i> is one of the following values:
* '''0:''' ''Title Case''
 
* '''1:''' ''All Words''
 
* '''2:''' ''First word''
 
* '''3:''' ''ALL UPPERCASE''
 
* '''4:''' ''all lowercase''
 
  
''If no case mode is specified, the function will default to using "Title Case". Title case will start each principal word with a capital. More detail regarding title case can be found [http://www.grammar-monster.com/lessons/capital_letters_title_case.htm here]''
+
<div style="margin-left: 20pt;"><table style="border-spacing:0px; border-collapse:collapse">
 +
<tr><td style="text-align:left; padding-right:20pt"><b>list</b></td><td>A list of strings, separated by semicolons</td></tr>
 +
<tr><td style="text-align:left; padding-right:20pt"><b>string</b></td><td>Sorts as strings (with smart number handling)</td></tr>
 +
<tr><td style="text-align:left; padding-right:20pt"><b>number</b></td><td>Sorts values as numbers (decimal or integer)</td></tr>
 +
<tr><td style="text-align:left; padding-right:20pt"><b>integer</b></td><td>Sorts values as integers</td></tr>
 +
<tr><td style="text-align:left; padding-right:20pt"><b>path</b></td><td>Sorts using a smart filename compare style</td></tr>
 +
<tr><td style="text-align:left; padding-right:20pt"><b>month</b></td><td>Sorts string month names (i.e. January, February, etc.)</td></tr>
 +
</table></div>
  
|- valign="top"
+
=== Calculated Fields and Search ===
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Examples
 
|style="background: #ecfeea; color: black; border: 1px solid black" | '''fixcase([album])'''<br>This will take the contents of the [album] field and present it with the specified capitalisation. As there is no specified mode here, the function defaults to 0, so, if an album is entered in the library as "Time Out Of Mind", the function will return "Time Out of Mind" (note the lower case "of")
 
  
<br>'''fixcase(MY ALbUm IS cAlLeD [album],4)'''<br>This would return "my album is called time out of mind"
+
Media Center's [[Search Language]] supports some simple numeric [[Search Language#Comparison_Operators|comparison operators]].
|}
+
Because expressions always evaluate as a String type, these operators would be unavailable for use in a search query to compare numeric values from a calculated expression field.
<div style="text-align:right;">([[#top|Back to top)]]</div>
+
In order to use the numeric comparison operators, a calculated expression field can be cast into one of the numeric types.
====Length(...): Returns the number of characters in a string====
+
In your numeric calculated fields, to allow the use Search's numeric comparison operators, add either of the casts:
{| style="width: 100%; border: 1px solid black" align="top" border="1" cellpadding="3"
 
|- valign="top"
 
! scope="row" style="white-space:nowrap; background: #A8E4A0; color: black; border: 1px solid black;" width=100 | Length()
 
| style="background: #ecfeea; color: black; border: 1px solid black" width=1200 | This function returns the number of characters in any given string.
 
|- valign="top"
 
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Construction
 
| style="background: #ecfeea; color: black; border: 1px solid black" | '''Length(String to count characters from)'''<br>''The ''"String to count characters from"'' can be plain text, a library field, or a combination of the two.''
 
|- valign="top"
 
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Examples
 
|style="background: #ecfeea; color: black; border: 1px solid black" | '''length([filename])'''<br>''This will count the characters in the [filename] field and return the result. Spaces count as characters, so, C:\My File.mp3 would return 14.
 
  
<br>'''if(isequal(length([filename]),68,6),68 Characters or more,Less than 68 Characters)'''<br>''Here, Length() has been combined with another two functions, "If()" and "IsEqual()". The expression compares the length of the filename against the number 68. If there are 68 or more characters in the filename, the expression will return "68 Characters or more", otherwise, it will return "Less than 68 Characters". If you are working with a device with filename length limitations, these functions can be used to create extremely useful expressions that could help with your device management.''
+
<div style="margin-left: 20pt"><span style="font-family: monospace,monospace; font-size:1em;">&datatype=[integer]</span></div>
|}
 
<div style="text-align:right;">([[#top|Back to top)]]</div>
 
====Left(...): Retrieves a specified number of characters from the left of a value====
 
{| style="width: 100%; border: 1px solid black" align="top" border="1" cellpadding="3"
 
|- valign="top"
 
! scope="row" style="white-space:nowrap; background: #A8E4A0; color: black; border: 1px solid black;" width=100 | Left()
 
| style="background: #ecfeea; color: black; border: 1px solid black" width=1200 | This function retrieves a specified number of characters from the left of any given value.
 
|- valign="top"
 
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Construction
 
| style="background: #ecfeea; color: black; border: 1px solid black" | '''Left(Value to get characters from,Number of characters to get)'''<br>''"Value to get characters from" can be plain text, a library field, or combination of both. If more characters than exist are requested, all available characters are returned.''
 
|- valign="top"
 
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Examples
 
|style="background: #ecfeea; color: black; border: 1px solid black" | '''left([filename],3)'''<br>''This will return the drive letter, colon and first back-slash from the filename. If asked to show more characters than actually exist, the expression will return the entire value, also, remember that spaces count as characters too.''
 
|}
 
<div style="text-align:right;">([[#top|Back to top)]]</div>
 
====Right(...): Retrieves a specified number of characters from the right of a value====
 
{| style="width: 100%; border: 1px solid black" align="top" border="1" cellpadding="3"
 
|- valign="top"
 
! scope="row" style="white-space:nowrap; background: #A8E4A0; color: black; border: 1px solid black;" width=100 | Right()
 
| style="background: #ecfeea; color: black; border: 1px solid black" width=1200 | This function retrieves a specified number of characters from the right of any given value.
 
|- valign="top"
 
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Construction
 
| style="background: #ecfeea; color: black; border: 1px solid black" | '''Right(Value to get characters from,Number of characters to get)'''<br>''"Value to get characters from" can be plain text, a library field, or combination of both. If more characters than exist are requested, all available characters are returned.''
 
|- valign="top"
 
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Examples
 
|style="background: #ecfeea; color: black; border: 1px solid black" | '''right([filename],3)'''<br>''This will return the last three characters from the filename. If asked to show more characters than actually exist, the expression will return the entire value, also, remember that spaces count as characters too.''
 
|}
 
<div style="text-align:right;">([[#top|Back to top)]]</div>
 
====RemoveLeft(...): Trims characters from the start of a value====
 
{| style="width: 100%; border: 1px solid black" align="top" border="1" cellpadding="3"
 
|- valign="top"
 
! scope="row" style="white-space:nowrap; background: #A8E4A0; color: black; border: 1px solid black;" width=100 | RemoveLeft()
 
| style="background: #ecfeea; color: black; border: 1px solid black" width=1200 | The output from this function will remove a specified number of characters from the start of any given value.
 
|- valign="top"
 
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Construction
 
| style="background: #ecfeea; color: black; border: 1px solid black" | '''RemoveLeft(Value to remove characters from,Number of characters to remove)'''
 
|- valign="top"
 
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Examples
 
|style="background: #ecfeea; color: black; border: 1px solid black" | '''removeleft([name],5)'''<br>''This would show the name field, with the first five characters removed. If asked to remove more characters than actually exist, the output will be blank, also, remember that spaces count as characters too.''.
 
|}
 
<div style="text-align:right;">([[#top|Back to top)]]</div>
 
====RemoveRight(...): Trims characters from the end of a value====
 
{| style="width: 100%; border: 1px solid black" align="top" border="1" cellpadding="3"
 
|- valign="top"
 
! scope="row" style="white-space:nowrap; background: #A8E4A0; color: black; border: 1px solid black;" width=100 | RemoveRight()
 
| style="background: #ecfeea; color: black; border: 1px solid black" width=1200 | The output from this function will remove a specified number of characters from the end of any given value.
 
|- valign="top"
 
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Construction
 
| style="background: #ecfeea; color: black; border: 1px solid black" | '''RemoveRight(Value to remove characters from,Number of characters to remove)'''
 
|- valign="top"
 
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Examples
 
|style="background: #ecfeea; color: black; border: 1px solid black" | '''removeright([name],5)'''<br>''This would show the name field, with the last five characters removed. If asked to remove more characters than actually exist, the output will be blank, also, remember that spaces count as characters too.''.
 
|}
 
<div style="text-align:right;">([[#top|Back to top)]]</div>
 
====Mid(...): Retrieves specified characters from a value.====
 
{| style="width: 100%; border: 1px solid black" align="top" border="1" cellpadding="3"
 
|- valign="top"
 
! scope="row" style="white-space:nowrap; background: #A8E4A0; color: black; border: 1px solid black;" width=100 | Mid()
 
| style="background: #ecfeea; color: black; border: 1px solid black" width=1200 | Mid() retrieves a specified number of characters from a specified starting point in any given string.
 
|- valign="top"
 
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Construction
 
| style="background: #ecfeea; color: black; border: 1px solid black" | '''Mid(Value to get characters from,Character to start at,Number of characters to get)'''
 
* '''Value to get characters from''': ''This can be a library field, plain text, or a combination of both.
 
* '''Character to start at''': ''This is a numerical pointer, and rather confusingly, the function treats the first character as zero and begins from there. If not specified, the function will default to zero.
 
* '''Number of characters to get''': ''If this value is not specified, the function will default to 1. -1 can be used to retrieve all available characters after the specified start point.
 
  
|- valign="top"
+
<div style="margin-left: 20pt"><span style="font-family: monospace,monospace; font-size:1em;">&datatype=[number]</span></div>
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Examples
 
|style="background: #ecfeea; color: black; border: 1px solid black" | '''mid(12345)'''<br>''As values for "Character to start at" and "Number of characters to get" have not been specified, they default to 0 and 1 respectively and the function returns the first character in the string, 1.''
 
  
<br>'''mid(12345,1,2)'''<br>''The start point has been specified as the second character in, and 2 characters have been asked for, the result here will be 23.''
+
to the end of the field's calculated expression.
  
<br>An example of Mid() being used to re-order a date field was given in answer to the question "[http://yabb.jriver.com/interact/index.php?topic=52809.0 Can I include seconds in "import date"?]"
+
=== Lists and Trees ===
|}
+
<div>
<div style="text-align:right;">([[#top|Back to top)]]</div>
+
[[File:Datatype_List.png|right]]
====Replace(...): Replace or remove strings from a value.====
+
The list of output in view categories and pane columns can be modified by forcing the data type to a List type.
{| style="width: 100%; border: 1px solid black" align="top" border="1" cellpadding="3"
+
Two things happen when the data type is List:
|- valign="top"
+
The values within a List type are split into their individual (semicolon-separated) list items
! scope="row" style="white-space:nowrap; background: #A8E4A0; color: black; border: 1px solid black;" width=100 | Replace()
+
The backslash character takes on a special meaning and becomes another form of separator that creates tree-like hierarchies,
| style="background: #ecfeea; color: black; border: 1px solid black" width=1200 | Quite simply, this function allows to search for a specified string in a specified value, and if found, remove the specified string, or replace it with another.
+
collapsible in panes columns and creates drill-down categories in any category view type (Standard View > Categories, Theater View, DLNA, Gizmo/WebGizmo).
|- valign="top"
+
Forcing an expression's type to <span style="font-family: monospace,monospace; font-size:1em;">list</span> causes this list item separation and hierarchy generation.
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Construction
+
Alternatively, forcing a List type to <span style="font-family: monospace,monospace; font-size:1em;">string</span> defeats this.
| style="background: #ecfeea; color: black; border: 1px solid black" | '''Replace(Value to check,String to check for,String to replace with)'''
+
Add the cast:
* '''Value to check''': ''This can be plain text, a library field, or combination of both.''
 
* '''String to check for''': ''Note that this check is <ins>case-sensitive</ins>''
 
* '''String to replace with''': ''Any instance of the "String to check for" will be replaced by this string. If not specified, any instance of the "String to check for" will be removed.''
 
|- valign="top"
 
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Examples
 
|style="background: #ecfeea; color: black; border: 1px solid black" | '''replace(My Sample String,S,Replaced )'''<br>''All instances of upper-case "S" will be replaced by the text "Replaced ", (note the trailing space), resulting in'' "My Replaced ample Replaced tring"
 
  
<br>'''replace(My Sample String,s,Replaced )'''<br>''The "Value to check" does not contain any lower-case "s", resulting in unchanged output'' "My Sample String"
+
<div style="margin-left: 20pt"><span style="font-family: monospace,monospace; font-size:1em;">&datatype=[list]</span></div>
  
<br>'''replace(My Sample String,/ Sample,stic)'''<br>''In this example, the space preceding the word Sample is to be included in the "String to check for". Remembering that, as discussed in the [[#Overview|Overview]], spaces that follow a comma are ignored unless escaped, an escaping forward slash is used to force the inclusion of the space in the check. The result here will be'' "Mystic String".
+
to the end of an expression to force an expression's output to be considered as a List type.
|}
+
Conversely, a List type may be forced into a String type by adding the cast:
<div style="text-align:right;">([[#top|Back to top)]]</div>
 
====Counter(...): Counts upwards in specified increments====
 
{| style="width: 100%; border: 1px solid black" align="top" border="1" cellpadding="3"
 
|- valign="top"
 
! scope="row" style="white-space:nowrap; background: #A8E4A0; color: black; border: 1px solid black;" width=100 | Counter()
 
| style="background: #ecfeea; color: black; border: 1px solid black" width=1200 | This function can be used to number objects sequentially, from a specified starting point, in specified increments. The counter resets itself to zero after five seconds of inactivity.<br>Counter() can exhibit a touch of wierdness when used in certain situations, which will be covered in the examples, that demonstrate why this one is not really a 'fits all' function.
 
|- valign="top"
 
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Construction
 
| style="background: #ecfeea; color: black; border: 1px solid black" | '''Counter(Number to start counting from,Increments to count up in)'''
 
  
* '''Number to start counting from''': ''This is optional. If not specified, the counter will start from one. If specified, the start value is inclusive, meaning that if a start value of five is specified, the first value the function returns will be five.''
+
<div style="margin-left: 20pt"><span style="font-family: monospace,monospace; font-size:1em;">&datatype=[string]</span></div>
* '''Increments to count up in''': ''This optional. If not specified, the counter will count up in increments of 1''
 
|- valign="top"
 
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Examples
 
|style="background: #ecfeea; color: black; border: 1px solid black" | '''counter()'''<br>This shows the function in its simplest form. The counter will start at one and count upwards in increments of 1.
 
  
<br>'''[[#PadNumber(...): Adds leading zeros to any given number|padnumber]](counter(370,2),4)'''<br>This expression shows a combined use of functions. Counter() will count up, in two's, starting from 370, and the padnumber function will pad the results to four figures, giving output values of 0370, 0372, 0374, etc. etc..
+
to the end of an expression.
 +
</div>
  
<br>'''Weirdness'''<br>Counter() works really really well, and really really efficiently when used to sequentially number static data fields. It is not designed to be used in a dynamically changing expression column in a file list. To demonstrate this, right click on a list column header and choose the option to "Add expression column". Use the first, simple expression above, and press OK. The column is presented and all the items in the list are now numbered in this column, but, see what happens when you run the cursor up and down the list? The counter function just keeps on going and going. Right click on the expression column header, and it will appear at the top of the selectable columns list with a tick beside it, click on it to remove the column. This same anomally appears when counter() is used in the "Rename, Move and Copy Files" tool. There may be a possible solution to this effect as seen in the renaming tool by using the CustomData(#) function, but only if the count is to start from 1.<br>Some interesting reading regarding the use of Counter() can be found in answer to "[http://yabb.jriver.com/interact/index.php?topic=48659.0 how to fill the NAME field with incrementing numbers?]" and "[http://yabb.jriver.com/interact/index.php?topic=50622.0 Prepending a consecutive number to titles as I copy them from MC13 to mp3 player]".
+
=== Sort Order ===
|}
+
<div>
<div style="text-align:right;">([[#top|Back to top)]]</div>
+
[[File:Datatype_Month.png|right]]
====RemoveCharacters(...): Removes specified characters from a given field or string====
+
Normally strings are sorted ASCII-betically with some smart numeric sorting.
{| style="width: 100%; border: 1px solid black" align="top" border="1" cellpadding="3"
+
But this form of sort may not always be desired.
|- valign="top"
 
! scope="row" style="white-space:nowrap; background: #A8E4A0; color: black; border: 1px solid black;" width=100 | <small>RemoveCharacters()</small>
 
| style="background: #ecfeea; color: black; border: 1px solid black" width=1200 | This function will remove specified characters from a given field or string using one of three specified modes. (Available in build 16.0.148 onwards.)
 
|- valign="top"
 
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Construction
 
| style="background: #ecfeea; color: black; border: 1px solid black" | '''RemoveCharacters(String to test,CharactersToTestFor,Mode)'''
 
  
* '''String to test''': ''This can be plain text, a library field, or a combination of the two.''
+
==== Sorting by Month ====
* '''Characters to test for''': ''series of characters, or strings of characters, placed all together between two commas, that are to be removed'' (note that this function is <ins>case sensitive</ins>)
+
Generally it is more useful to see month names sorting such that January sorts before April, instead of alphabetically where April would sort before January.
* '''Mode''': ''There are four available modes, each detailed below. Note that if no mode is specified, the function will default to using mode 0 (remove all instances)
+
Forcing an expression's type to Month forces string month values to be treated instead as their equivalent numerical month numbers.
''Available Modes:''
+
For example, the first month January and the third month March sort before the fourth month April.
* 0: Remove all instances
+
Add the cast:
* 1: Remove from the beginning only
 
* 2: Remove from the end only
 
* 3: Remove from each end
 
|- valign="top"
 
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Examples
 
|style="background: #ecfeea; color: black; border: 1px solid black" | '''RemoveCharacters(Paper,Ppr,0)'''<br>This will result in "ae" as P, p and r are removed.
 
  
'''RemoveCharacters(Paper,Ppr,1)'''<br>This will result in "aper" as "mode 1" has been specified, and the capital P is removed from the start.
+
<div style="margin-left: 20pt"><span style="font-family: monospace,monospace; font-size:1em;">&datatype=[month]</span></div>
  
'''RemoveCharacters(Paper,Ppr,2)'''<br>This will result in "Pape" as "mode 2" has been specified, and the lower case r is removed from the end.
+
to the end of an expression to force an expression's output to be sorted by numeric month values.
  
'''RemoveCharacters(Paper,Ppr,3)'''<br>This will result in "ape" as "mode 3" has been specified, the capital P is removed from the start, and the lower case r is removed from the end.
+
==== Sorting by Path ====
  
'''RemoveCharacters([artist],/(/),)'''<br>This will remove any opening or closing brackets from anywhere within the [artist] field. Note how the brackets are 'escaped' as discussed in the [[#Overview|'Overview']] section earlier.
+
Path data types sort using smart filename comparisons.
|}
 
<div style="text-align:right;">([[#top|Back to top)]]</div>
 
<br><br>
 
  
===Functions for the manipulation and creation of list type fields===
+
XXX: Note: This section is incompleteI cannot distingish any difference between using a datatype of <span style="font-family: monospace,monospace; font-size:1em;">path</span> vs. <span style="font-family: monospace,monospace; font-size:1em;">string</span>. It seems <span style="font-family: monospace,monospace; font-size:1em;">path</span> sort order is always engaged.
The default MEDIA CENTER library contains many fields that are referred to as "list type" fields. Users are also able to add their own "list type" fields to their libraries. A list type field contains one or more text items seperated by semi-colons. The semi-colons are referred to as the 'delimiter' and when displayed in a view category, text items seperated by semi-colons are displayed in a list of seprately selectable items. The "Keywords" field is a classic example of a list type field, which demonstrates how list type fields allow a single file to be tagged with many different keywords, as opposed to a 'standard' field, such as 'Genre', where a single file can only be tagged with a single genreThe following functions provide the ability to combine or build custom list type fields using the default semi-colon delimiter, or a specified delimiter, count the number of items contained in a given list, or extract a numbered entry from within a list. Two of the functions listed in this section are used to create "list type" data from two or more existing sources and could reasonably be considered to be functions more suited to those who are very familiar with MEDIA CENTER and how it gets its job done. If these functions are used to create a new 'calculated data' library field, they will not function as 'list type' fields unless the field is first created as a "User Data" field, with "List Type" specified. After creating the field in this way, it is possible to go back and edit the field, changing it to "calculated data" and entering an expression to be used. The [http://yabb.jriver.com/interact/index.php?topic=54226.msg374211#msg374211 "Eureka moment"] occurred in November 2009.
 
====ListBuild(...): Build a list from a series of values====
 
{| style="width: 100%; border: 1px solid black" align="top" border="1" cellpadding="3"
 
|- valign="top"
 
! scope="row" style="white-space:nowrap; background: #A8E4A0; color: black; border: 1px solid black;" width=100 | ListBuild()
 
| style="background: #ecfeea; color: black; border: 1px solid black" width=1200 | This function provides the ability to create a single list from many different sources and allows a list delimiter to be specified. It has two modes that can be applied and are detailed below. Of these two modes, mode "0" (Combine all values) should be avoided. It has been included for 'function completeness' only, and when used, can produce some very strange results that do not filter as expected. In order for the data generated by this function to be treated as list data, the [[#Specify data types for expression based fields|'datatype']] must be specified as [list].
 
|- valign="top"
 
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Construction
 
| style="background: #ecfeea; color: black; border: 1px solid black" | '''ListBuild(Mode,Delimiter,Items,To,Include)'''<br>
 
'''Mode:''' ''There are two different modes available:
 
* '''0''': ''combine all values. NOTE: <ins>This mode should be avoided as there is no recorded practical use for it, and it's behaviour can be unpredictable.</ins>''
 
* '''1''': ''combine non-empty values''
 
  
'''Delimiter''': ''The character used here will be used as a delimiter between each of the specified list items. To be clear, the keywords field uses a semi-colon delimiter by default; if a list is built using keywords and genre, and the specified delimiter is a back slash, it will be used between the keywords and genre fields when joining them, the semi-colons in the keywords field would not be altered. For example, if [keywords] contained "these;are;keywords" and [genre] contained "Rock", and these two were joined using ListBuild with a "\" specified as the delimiter, the resulting data would be "These;are;keywords\Rock". The real beauty and power of this function can be released when expressions are nested into the ListBuild instructions. For example, "listbuild(1,\,replace([keywords],;,\),[genre]" would return the data "These\are\keywords\Rock"''
+
Add the cast:
<br>'''Items To Include''': ''This can be any number of specified text entries, expressions, or library fields, seperated by commas''
 
|- valign="top"
 
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Examples
 
|style="background: #ecfeea; color: black; border: 1px solid black" | '''listbuild(1,;,[keywords],[genre])&datatype=[list]'''<br>''This will return a semi-colon delimited list containing all keywords and genres. If either keyords or genre is empty, they will be ignored, so, the data returned for a file with no keywords, and a genre of "Rock" would be simply "Rock".''
 
  
<br>'''listbuild(1,\,[genre],[album artist (auto)],[album])&datatype=[list]'''<br>''When MEDIA CENTER encounters a back slash character in a list type field, it 'nests' the data in the list. Think of this in exactly the same way as Windows reads file paths, each back slash is another folder along the file path, and in a MEDIA CENTER list type view category, each back slash creates a virtual folder, and each semi-colon starts a new list entry, which means that effective browsing trees can be created using this knowledge. In the example shown here, a list of genres would be created, and each genre is able to be expanded to reveal a list of artists, which in turn can be expanded to reveal albums by that particular artist in that genre. So, now that this is getting interesting, there's an issue with this example. If a file has no specified [genre], the value is ignored, and the [album artist (auto)] value is placed on the root of the virtual tree, which means that the completely collapsed list contains a mixture of [genre] and [album artist (auto)]. The next example demonstrates how to clean that up.''
+
<div style="margin-left: 20pt"><span style="font-family: monospace,monospace; font-size:1em;">&datatype=[path]</span></div>
  
<br>'''listbuild(1,\,if([[#IsEmpty(...): Tests to see if a field is empty|isempty]]([genre]),!No Genre Applied,[genre]),[album artist (auto)],[album])&datatype=[list]'''<br>''Here, the previous example has been improved by nesting an [[#IsEmpty(...): Tests to see if a field is empty|IsEmpty()]] function into the listbuild function. The result is that all files without a specified genre are placed in a group at the top of the virtual tree called "!No Genre Applied", and the rest of the root consists of existing genre values, which is much tidier.
+
to the end of an expression to force an expression's output to be smart-sorted by path components.
|}
 
<div style="text-align:right;">([[#top|Back to top)]]</div>
 
====ListCombine(...): Combines two delimited lists into a single delimited list====
 
{| style="width: 100%; border: 1px solid black" align="top" border="1" cellpadding="3"
 
|- valign="top"
 
! scope="row" style="white-space:nowrap; background: #A8E4A0; color: black; border: 1px solid black;" width=100 | ListCombine()
 
| style="background: #ecfeea; color: black; border: 1px solid black" width=1200 | Unlike the [[#ListBuild(...): Build a list from a series of values|ListBuild]] function above, which can be used to create a list from any number of varying sources, ListCombine() is used to merge two specified lists into one. In order for the data generated by this function to be treated as list data, the [[#Specify data types for expression based fields|'datatype']] must be specified as [list].
 
|- valign="top"
 
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Construction
 
| style="background: #ecfeea; color: black; border: 1px solid black" | '''ListCombine(First list,Second list,Input Delimiter,Output Delimiter)'''<br>
 
'''First List''' ''and'' '''Second List''' are specified library fields.
 
  
'''Input Delimiter''': ''This is the value that will be used to join the two specified lists. The value is optional, and if not specified, the function will default to using a semi-colon.''
+
</div>
  
'''Output Delimiter''': ''This value is also optional. If specified, the function parses the output list (the result of the two lists, joined by the input delimiter) and replaces each occurrence of the input delimiter with the specified output delimiter.
+
== Expressions and Search ==
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The expression language is fully available to the search query engine (Search, Set rules for file display, etc.).
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Examples
+
This allows creation of more complex search queries than would otherwise be possible.
|style="background: #ecfeea; color: black; border: 1px solid black" | '''listcombine([people],[places])&datatype=[list]'''<br>''The result here would be a single, semi-colon delimited list containing all the values from the [people] and [places] fields.''
+
An expression-based search query is any valid expression that produces a zero or non-zero numeric output.
 +
The syntax of the query is:
  
* [people] contains ''Family\Mum;Family\Dad;Family\Gran''
+
<div style="margin-left: 20pt"><span style="font-family: monospace,monospace; font-size:1em;"><b>[=</b><i>expression</i><b>]=</b><i>numval</i></span></div>
* [places] contains ''United Kingdom\Scotland\Edinburgh;United Kingdom\Scotland\Edinburgh\Edinburgh Castle''
 
* The output list from the above expression would be: ''Family\Mum;Family\Dad;Family\Gran'''<ins>;</ins>'''United Kingdom\Scotland\Edinburgh;United Kingdom\Scotland\Edinburgh\Edinburgh Castle'' (the specified "listcombine delimiter" shown in bold and underlined)
 
  
<br>'''listcombine([people],[places],\)&datatype=[list]'''<br>''Here, the resulting list will be the [people] and [places] lists joined using a back slash. Remember that MEDIA CENTER interprets back slashes as a folder hierarchy when displaying list type fields in a view category pane.''
+
where expression is any valid expression, and numval is the expected numeric output produced by the expression.
 +
The expression is evaluated against the current list of available files and the expression output numerically compared against numval.
 +
All files for which the comparison is true are returned as part of the file list produced by the query and all files that fail the comparison are winnowed from the file list.
  
* [people] contains ''Family\Mum;Family\Dad;Family\Gran''
+
The following example illustrates an expression-based search query:
* [places] contains ''United Kingdom\Scotland\Edinburgh;United Kingdom\Scotland\Edinburgh\Edinburgh Castle''
 
* The output list from the above expression would be: ''Family\Mum;Family\Dad;Family\Gran'''<ins>\</ins>'''United Kingdom\Scotland\Edinburgh;United Kingdom\Scotland\Edinburgh\Edinburgh Castle'' (the specified "listcombine delimiter" shown in bold and underlined)
 
  
<br>'''listcombine([people],[places],\,;)&datatype=[list]'''<br>''Finally, a semi-colon output delimiter has been specified, therefore, all back slashes will be replaced by semi-colons, and the resulting list will be a single, flat list containing all the text entries from each field:''
+
<div style="margin-left: 20pt"><span style="font-family: monospace,monospace; font-size:1em;">[=ismissing([filename (path)]\Folder.jpg)]=1</span></div>
  
* [people] contains ''Family\Mum;Family\Dad;Family\Gran''
+
The [[Test_and_Comparison_Functions#IsMissing|IsMissing()]] function is run using the file name argument <span style="font-family: monospace,monospace; font-size:1em;">[filename (path)]</span> appended by <span style="font-family: monospace,monospace; font-size:1em;">\Folder.jpg</span>,
* [places] contains ''United Kingdom\Scotland\Edinburgh;United Kingdom\Scotland\Edinburgh\Edinburgh Castle''
+
and returns a Boolean value <span style="font-family: monospace,monospace; font-size:1em;">1</span> for files that are missing, and this <span style="font-family: monospace,monospace; font-size:1em;">1</span> is compared against the value <i>numval</i>.
* The output list from the above expression would be: ''Family;Mum;Family;Dad;Family;Gran'''<ins>;</ins>'''United Kingdom;Scotland;Edinburgh;United Kingdom;Scotland;Edinburgh;Edinburgh Castle'' (the specified "listcombine delimiter" shown in bold and underlined)
+
All these files where there was a successful comparison are returned in the file list,
|}
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and all those for which the expression produced <span style="font-family: monospace,monospace; font-size:1em;">0</span> are filtered from the file list.
<div style="text-align:right;">([[#top|Back to top)]]</div>
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By inverting the comparison and using a <span style="font-family: monospace,monospace; font-size:1em;">0</span> numval, the set of files remaining in the file list would be those that did not match.
====ListCount(...): Returns the number of items in a delimited list====
 
{| style="width: 100%; border: 1px solid black" align="top" border="1" cellpadding="3"
 
|- valign="top"
 
! scope="row" style="white-space:nowrap; background: #A8E4A0; color: black; border: 1px solid black;" width=100 | ListCount()
 
| style="background: #ecfeea; color: black; border: 1px solid black" width=1200 | ListCount is used to return the number of items that exist in any given field, using any given delimiter.
 
|- valign="top"
 
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Construction
 
| style="background: #ecfeea; color: black; border: 1px solid black" | '''ListCount([Field to count],Delimiter to use)'''<br>
 
'''Field to count''': ''Typically, this will be a list type field, but this is not compulsory. The data in any field can be parsed using any chosen delimiter''
 
  
'''Delimiter to use''': ''This is optional. If not specified, the function will default to using a semi-colon delimiter. Anything can be specified as a delimiter, from a single character to a whole word or words.''
+
== HTML Font Properties ==
|- valign="top"
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The expression language recognizes a limited set of HTML font properties and attributes. These can be used to set font styles in most text drawing areas, such as captions, thumbnail text and in the configuration of Theater View.
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Examples
+
HTML tags are used by surrounding the desired content with an opening and closing tag, in the form of:
|style="background: #ecfeea; color: black; border: 1px solid black" | '''listcount([People])'''<br>
 
''No delimiter has been specified here, therefore the function will default to using a semi-colon. The result here will match the number of people shown in a properly tagged photo. Note that the function is smart, so, if a file has no [People] tag, the function will return zero (0), and if it has [People] data, but no semi-colon, the function will return one (1).''
 
  
<br>'''listcount([filename (path)],\)'''<br>
+
: <span style="font-family: monospace,monospace; font-size:1em;"><<i>tag</i>><i>desired content</i><//<i>tag</i>></span>
''This function can be used to count the directories in a filepath by specifying a back slash as the delimiter.''
 
  
<br>'''listcount([keywords],!People)'''<br>
+
The supported HTML tags are:
''This basic expression can be used as a building block to create a more complex expression to count the number of people tagged in a photo. the full expression can be seen [http://yabb.jriver.com/interact/index.php?topic=43975.msg301390#msg301390 here]. That thread is actually the release thread for the 'new' nesting feature, introduced in 2007, and although 2 pages long, is worth a read as it contains some quite useful information.''
+
<div style="margin-left: 20pt;"><table style="border-spacing:0px; border-collapse:collapse">
|}
+
<tr><td style="text-align:left; padding-right:20pt"><b><nowiki><b></nowiki></b></td><td>Bold</td></tr>
<div style="text-align:right;">([[#top|Back to top)]]</div>
+
<tr><td style="text-align:left; padding-right:20pt"><b><nowiki><i></nowiki></b></td><td>Italics</td></tr>
====ListItem(...): Returns a specified value from a delimited list====
+
<tr><td style="text-align:left; padding-right:20pt"><b><nowiki><u></nowiki></b></td><td>Underline</td></tr>
{| style="width: 100%; border: 1px solid black" align="top" border="1" cellpadding="3"
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<tr><td style="text-align:left; padding-right:20pt"><b><nowiki><font></nowiki></b></td><td>Font properties (see attributes below)</td></tr>
|- valign="top"
+
</table></div>
! scope="row" style="white-space:nowrap; background: #A8E4A0; color: black; border: 1px solid black;" width=100 | ListItem()
 
| style="background: #ecfeea; color: black; border: 1px solid black" width=1200 | This function numbers list items starting from zero and returns the value of a specifically numbered item.
 
|- valign="top"
 
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Construction
 
| style="background: #ecfeea; color: black; border: 1px solid black" | '''ListItem([Field],Number of item to retrieve,Field delimiter to use)'''
 
  
* '''Field''': ''The function will accept any given field, though is more typically used with list type fields.''
+
The <b>font</b> tag supports the following attributes:
* '''Number of item to retrieve''': ''The number of the item in the list to retrieve. The list items are numbered starting from zero.''
+
<div style="margin-left: 20pt;"><table style="border-spacing:0px; border-collapse:collapse">
* '''Field delimiter to use''': ''This is optional. If not specified, the function will default to using a semi-colon delimiter. Anything can be specified as a delimiter, from a single character to a whole word or words.''
+
<tr><td style="text-align:left; padding-right:20pt"><b>alpha</b></td><td>Sets alpha-blending percentage (0 - 100)</td></tr>
|- valign="top"
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<tr><td style="text-align:left; padding-right:20pt"><b>color</b></td><td>Sets the foreground color (RGB hex values from 00 to ff in the form of rrggbb)</td></tr>
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Examples
+
<tr><td style="text-align:left; padding-right:20pt"><b>bgcolor</b></td><td>Sets the background color (same values as color)</td></tr>
|style="background: #ecfeea; color: black; border: 1px solid black" | '''listitem([filename],0,\)'''<br>''This function will return a file's drive letter plus colon. Note that the same result could be achieved by using '''[[#Left(...): Retrieves a specified number of characters from the left of a value|left]]([filename],2)''', there is no 'right' or 'wrong' with these things, just personal preference, or 'what works for you'. A good rule of thumb is to use the simplest possible way to get to your goal, as less typing is better, and the more simple the expression, the easier it is to follow.''
+
<tr><td style="text-align:left; padding-right:20pt"><b>face</b></td><td>Sets the font face (a font name)</td></tr>
 +
<tr><td style="text-align:left; padding-right:20pt"><b>size</b></td><td>Sets the font size (a percentage scaling value)</td></tr>
 +
</table></div>
  
<br>'''listitem([filename],2,\)'''<br>''Here, the result will be the name of the second directory along a file's folder path from the drive root. C:\Folder1\Folder2\ are itemised as 0\1\2\, so rather confusingly, the second directory is actually the third item in the back slash delimited path.''
+
Any combination of HTML tags and font attributes can be used.
 +
An HTML tag must have an opening and closing tag.
 +
Nesting is allowed, but be sure to properly balance like opening and closing tags.
 +
Attribute values must be double quoted. The closing tag's forward slash requires escapement with an extra forward slash.
 +
The following examples illustrate using HTML font properties:
  
<br>'''listitem([filename (path)],math(listcount([filename (path)],\)-1),\)'''<br>''This expression uses the [[#Math(...): Evaluates a given mathematical formula|math()]] and [[#ListCount(...): Returns the number of items in a delimited list|listcount()]] functions to find the "Number of item to retrieve" value. listcount() returns the total number of directories in the path, and the math function subtracts one from this number (because listcount() starts counting at one, but listitem starts counting from zero), this number is then used by the listitem function. The result will be the name of the parent folder of each file. Setting the expression up in this way means that the result will always be reliable regardless of the number of folders in the filepath as the expression will work all of this out for itself.''
+
: <span style="font-family: monospace,monospace; font-size:1em;"><nowiki><i>This is in italics<//i></nowiki></span>
|}
 
<div style="text-align:right;">([[#top|Back to top)]]</div>
 
<br><br>
 
===Functions that perform specific tasks===
 
The functions in this group, with the possible exception of the math() function, are used to carry out very specific tasks, or for use in very specific areas of MEDIA CENTER.
 
====Now(...): Retrieve and display the system date====
 
{| style="width: 100%; border: 1px solid black" align="top" border="1" cellpadding="3"
 
|- valign="top"
 
! scope="row" style="white-space:nowrap; background: #A8E4A0; color: black; border: 1px solid black;" width=100 | Now()
 
| style="background: #ecfeea; color: black; border: 1px solid black" width=1200 | Now() will return the raw system date. "raw" data is discussed in the [[#Field|Field]] description, and also in the introduction to the [[#Change how existing data is displayed using Format functions|"Format"]] functions. As MEDIA CENTER's raw date data is illegible, this function needs to be used with the "[[#FormatDate(...): Formats a date value in a specified manner|FormatDate()]]" function, which allows the current date, and time, if desired, to be presented in many different styles.
 
|- valign="top"
 
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Construction
 
| style="background: #ecfeea; color: black; border: 1px solid black" | '''Now()'''
 
|- valign="top"
 
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Examples
 
|style="background: #ecfeea; color: black; border: 1px solid black" | '''formatdate(now(),date)'''<br>''Returns the current date, without the time, formatted according to the system settings on which the function is running.''
 
  
<br>'''formatdate(now(),dddd dd MMMM yyyy) [[#PadNumber(...): Adds leading zeros to any given number|padnumber]](formatdate(now(),hour),2):[[#PadNumber(...): Adds leading zeros to any given number|padnumber]](formatdate(now(),minute),2)'''<br>
+
: <span style="font-family: monospace,monospace; font-size:1em;"><nowiki><i><b>And this is bold and italic<//b><//i></nowiki></span>
''Here, three seperate expressions have been strung together to return a fully formatted current date and time:'' '''''Sunday 26 September 2010 14:04'''''
 
  
<br>'''[=isequal(formatdate([date imported,0],MM//yyyy),formatdate(now(),MM//yyyy)]=1 ~sort=[Date Imported]-d'''<br>
+
: <span style="font-family: monospace,monospace; font-size:1em;"><nowiki><b>The<font color=&quot;ff0000&quot; size=&quot;80&quot; alpha=&quot;50&quot;> Great <//font>Gatsby<//b></nowiki></span>
''MEDIA CENTER comes with a stock smartlist titled "Imported This Month". On the face of it, this could be a handy list of files, but is actually rather misleading. Closer inspection of this stock smartlist reveals that it is not actually listing files "Imported This Month", but instead, listing those files that have been imported in the past 31 days by using the following rule: [Date&nbsp;Imported]=<31d&nbsp;~sort=[Date&nbsp;Imported]-d<br>
 
This would mean that if you were to view that list on the second of March, you could potentially be looking at a list of files imported during three different months. The example in bold above corrects this anomaly by comparing the month/year imported with the current month/year, and only lists the file if the two match.<br>
 
This is also an example of how to use an expression in a search rule, as detailed in "[[#When, Where and How to use expressions|When, Where and How to use expressions]]"
 
  
<br>''<ins>[http://yabb.jriver.com/interact/index.php?topic=56487.0 This topic]</ins> expands on the example above a little by showing how to construct rules that return files that have been played or imported today or yesterday.''
+
== Expression Editors ==
|}
+
There are a couple of variations of dialog or edit field used to enter expressions.
<div style="text-align:right;">([[#top|Back to top)]]</div>
+
Some allow multi-line expressions, while others are single line, but can be expanded to multi-line editors.
====Math(...): Evaluates a given mathematical formula====
+
Unfortunately, some single-line editors flatten multi-line expressions into a single line, replacing the newlines with spaces.
{| style="width: 100%; border: 1px solid black" align="top" border="1" cellpadding="3"
 
|- valign="top"
 
! scope="row" style="white-space:nowrap; background: #A8E4A0; color: black; border: 1px solid black;" width=100 | Math()
 
| style="background: #ecfeea; color: black; border: 1px solid black" width=1200 | Math() can perform mathematical functions from the most simple to very complex. On the face of it, this might not appear to be all that useful, after all, Windows ships with Calc.exe does it not? However, where this comes into its own, is that the numbers to be used for the math formula can be derived from expressions nested within the Math() function, and now this particular function gets a little more interesting.
 
|- valign="top"
 
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Construction
 
| style="background: #ecfeea; color: black; border: 1px solid black" | '''Math(Formula to evaluate)'''
 
|- valign="top"
 
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Examples
 
|style="background: #ecfeea; color: black; border: 1px solid black" | '''math(10+4)'''<br>''This will return the answer, 14. Hardly earth shattering, but demonstrates the function working at its simplest level.
 
  
<br>'''math(10+2*25)''' & '''math((10+2)*25)'''<br>''The results here are 60 & 300 respectively, demonstrating that the math() function correctly honours the priorities of mathematical operators.''
+
== Acknowledgements ==
 +
A big tip of hat to [[User:Marko|marko]] who tackled the enormous challenge of documenting the MC Expression Language in detail. His work was instrumental and through which has brought clarity and great assistance to Media Center users worldwide.
  
<br>'''listitem([filename (path)],<ins>''math(listcount([filename (path)],\)-1)''</ins>,\)'''<br>''Here, a combination of math() and [[#ListCount(...): Returns the number of items in a delimited list|ListCount()]] are used to generate the number required by the [[#ListItem(...): Returns a specified value from a delimited list|ListItem()]] function. The math function has been asked to subtract 1 from the number returned by the ListCount() function, and the result is then used by ListItem to output its result, which in this case, would be the parent folder name for the specific file.''
+
Also, a huge thanks to user [[User:MrC|MrC]] who built [[Expression_Language_Archive|the amazing and long-lived previous version of this page]], upon which this is still heavily based.
  
<br>'''MEDIA CENTER and "Zero = Null"'''<br>MEDIA CENTER makes special use of the number zero in integer fields. All of that, and the work around to use, can be found in <ins>[http://yabb.jriver.com/interact/index.php?topic=58110.0 this topic]</ins>.
+
The current caretaker of this documentation is forever in their debts.
|}
 
<div style="text-align:right;">([[#top|Back to top)]]</div>
 
====Hexify(...): Hexifies a string to make it suitable for website usage====
 
{| style="width: 100%; border: 1px solid black" align="top" border="1" cellpadding="3"
 
|- valign="top"
 
! scope="row" style="white-space:nowrap; background: #A8E4A0; color: black; border: 1px solid black;" width=100 | Hexify()
 
| style="background: #ecfeea; color: black; border: 1px solid black" width=1200 | ''The only place this function is likely to be used is in the "Link Manager". Websites often don't like spaces in their addresses, and punctuation could confuse a site's search engine. Hexify attempts to take care of this by replacing spaces and punctuation with web friendly alternatives. For example, Bob Dylan would become Bob%20Dylan.''
 
|- valign="top"
 
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Construction
 
| style="background: #ecfeea; color: black; border: 1px solid black" | '''Hexify(Value to hexify)'''
 
|- valign="top"
 
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Examples
 
|style="background: #ecfeea; color: black; border: 1px solid black" | '''hexify([artist] - [album])'''<br>Oasis - (What's The Story) Morning Glory? becomes: ''Oasis%20-%20%28What%27s%20The%20Story%29%20Morning%20Glory%3F''
 
|}
 
<div style="text-align:right;">([[#top|Back to top)]]</div>
 
====CustomData(...): Sequence numbering when renaming files====
 
{| style="width: 100%; border: 1px solid black" align="top" border="1" cellpadding="3"
 
|- valign="top"
 
! scope="row" style="white-space:nowrap; background: #A8E4A0; color: black; border: 1px solid black;" width=100 | CustomData()
 
| style="background: #ecfeea; color: black; border: 1px solid black" width=1200 | The official description for this function goes as follows: ''"Returns custom data stored in a file array (used primarily for internal uses)."'' There is no recorded practical use for this function, with the exception of using it with a hash symbol in the library tool called "Rename, Move, & Copy Files...". When used in the directory or filename rules of this tool, this function will number the files in the list from first to last, starting at number one. As long as any desired numbering is to begin at one, this function is a reasonable alternative to combat the wierdness demonstrated by the [[#Counter(...): Counts upwards in specified increments|Counter()]] function, and could be particularly useful when renaming image files. If the numbering is required to start counting from anywhere other than one, then [[#Counter(...): Counts upwards in specified increments|Counter()]] will need to be used, taking the wierdness and its work arounds into account.
 
|- valign="top"
 
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Construction
 
| style="background: #ecfeea; color: black; border: 1px solid black" | '''CustomData(#)'''
 
|- valign="top"
 
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Examples
 
|style="background: #ecfeea; color: black; border: 1px solid black" | '''[[#PadNumber(...): Adds leading zeros to any given number|padnumber]](customdata(#),4)_Christmas Party 2007'''<br>''It's important to remember that this function will only work when used as part of the renaming rule for either filename or directory (or both) within the "Rename, Move, & Copy Files..." tool. In this example, imagine 324 photos from the Christmas party of 2007 were selected for renaming, and this expression was entered into the filename field. The resulting filenames would be 0001_Christmas Party 2007.jpg through to 0324_Christmas Party 2007.jpg. Note how the "[[#PadNumber(...): Adds leading zeros to any given number|padnumber()]]" function has been used to add the leading zeros.
 
|}
 
<div style="text-align:right;">([[#top|Back to top)]]</div>
 
====Tag(...): Returns a physical file tag (rather than looking in the database)====
 
{| style="width: 100%; border: 1px solid black" align="top" border="1" cellpadding="3"
 
|- valign="top"
 
! scope="row" style="white-space:nowrap; background: #A8E4A0; color: black; border: 1px solid black;" width=100 | Tag()
 
| style="background: #ecfeea; color: black; border: 1px solid black" width=1200 | This function originally came into being as a need arose for there to be a way to re-import the exif date information from image files without affecting any other tags. To that end, the function works well, but that's really where it's functionality ends. Success with any other fields has been extremely limited indeed. The main reason for this is because, when using this function to query specific tag data blocks in an image file, the fields referenced by the tag() function must be spelled ''exactly'' as they appear in the tag block within the file, and yes, they ''are'' case sensitive. It is also extremely important to know that when building a file list that contains a "Tag()" derived column, MEDIA CENTER will be inordinately slower, <ins>1000's of times slower</ins>, in building that list than it would be without the "Tag()" column. This is because each and every file in the list must be queried individually for the contents of the specified tag. This particular function is best used using the "inline editing" method outlined in the "[[#When, Where and How to use expressions|When, Where and How to use expressions]]" section of this page, to pull the desired data into the main library database and then reference the information from the database.
 
|- valign="top"
 
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Construction
 
| style="background: #ecfeea; color: black; border: 1px solid black" | '''Tag(Field to read from the file)'''<br>Specific tag data blocks from jpg files can also be referenced:<br>'''Tag(Tag Block To Query: Field to read from the tag block)'''
 
  
* Field to read from the file: Not case sensitive in all scenarios, but always case sensitive when targetting specific tag data blocks within jpg files.
+
[[Category:Frequently Asked Questions]]
* Tag blocks that can be queried from within jpg files are:
+
[[Category:Developer]]
** EXIF
+
[[Category:Expression Language]]
** XMP
 
** IPTC
 
** MJMD
 
|- valign="top"
 
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Examples
 
|style="background: #ecfeea; color: black; border: 1px solid black" | '''tag(artist)'''<br>''This will return the artist information from a file if that file contains the artist tag''
 
 
 
<br>'''tag(Gapless Header)''' or '''tag(Gapless Footer)'''<br>''These two expressions allow gapless information to be queried from mp3 files.''
 
 
 
<br>'''tag(exif: Date)'''<br>''This will return the raw date data from the EXIF data saved inside a jpg file. If this expression is used to import the data into MEDIA CENTER's default [Date] field, MEDIA CENTER will format the info into legible date information automatically. If importing into a custom field, wrap the tag() function inside a [[#FormatDate(...): Formats a date value in a specified manner|FormatDate()]] function like so: '''formatdate(tag(exif: Date),datetime)'''.''<br>''Note that "tag(exif: date)" will not return any result as the tag to query value is case sensitive and must be entered as "Date"''
 
|}
 
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====TVInfo(...): Returns television-specific information about a file====
 
{| style="width: 100%; border: 1px solid black" align="top" border="1" cellpadding="3"
 
|- valign="top"
 
! scope="row" style="white-space:nowrap; background: #A8E4A0; color: black; border: 1px solid black;" width=100 | TVInfo()
 
| style="background: #ecfeea; color: black; border: 1px solid black" width=1200 | Used to retieve and display specified televison information for a file.
 
|- valign="top"
 
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Construction
 
| style="background: #ecfeea; color: black; border: 1px solid black" | '''TVInfo(Information to retrieve)'''
 
'''Information to retrieve''': ''The options available for use here are:''
 
 
 
* '''IsProgram''': ''Tests whether the file is a program or not. (Returns 0 or 1)''
 
* '''IsGuideProgram''': ''Tests whether the file is a guide program or not. (Returns 0 or 1)''
 
* '''IsRecordedProgram''': ''Tests whether the file is a recorded program or not. (Returns 0 or 1)''
 
* '''NameDisplay''': ''Returns the name.''
 
* '''NameDisplayWithDate''': ''Returns the name + date.''
 
* '''SeriesDisplay''': ''Returns the series name.''
 
* '''TimeDisplay''': ''Shows the start time of a program using the system time format, but uses "Showing" if the program is on now.''
 
* '''TimeDisplayNoOnNow''': ''Shows the start time of a program using the system time format, without special handling for programs on now''
 
* '''SizeDisplay''': ''Returns the duration, formatted nicely for a television program.''
 
* '''WatchedDisplay''': ''Watched information, like no, yes, 80%, etc.''
 
 
 
|- valign="top"
 
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Examples
 
|style="background: #ecfeea; color: black; border: 1px solid black" | '''TVInfo(namedisplay)'''<br>Click on "<ins>T</ins>ools > Options > Theater View", then click on "Customize file info panel", then choose "Television Program" from the drop-list at the top. It is then possible to use this function to tailor the information displayed on screen in Theater view when looking at TV programs. Some of the default items already utilise this function offering real world, real time examples of their usage.
 
* TV programs use the field "Date Recorded" to store the program time.
 
* The "Date" field is the original air / production date.
 
|}
 
<div style="text-align:right;">([[#top|Back to top)]]</div>
 
====Note(...): Retrieve information from a note====
 
{| style="width: 100%; border: 1px solid black" align="top" border="1" cellpadding="3"
 
|- valign="top"
 
! scope="row" style="white-space:nowrap; background: #A8E4A0; color: black; border: 1px solid black;" width=100 | Note()
 
| style="background: #ecfeea; color: black; border: 1px solid black" width=1200 |  Since build 14.0.111, [http://yabb.jriver.com/interact/index.php?topic=54548.0 MEDIA CENTER has shipped with a "Notes" feature.] One of the many uses available via notes is the ability to store contact information, and that information can be labelled. Labels are typical contact information labels such as "Home phone", "Work phone", "Email" etc. etc.. This function can retrieve and display the contents of specified labels from a note.
 
|- valign="top"
 
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Construction
 
| style="background: #ecfeea; color: black; border: 1px solid black" | '''Note(Field Label,Field Type,Occurrance)'''
 
 
 
* '''Field Label''': ''There are too many labels to list here. To see the available labels, select some text in a note and right click that selected text, then hover the cursor over "Set Field" to see the list of available labels.''
 
* '''Field Type''': ''If the specified label was, for example, "Phone", then the "Type" could be "Home" or "Business" or any of the other available "Phone" types. This value is optional, and if not specified, the function will default to the first type encountered.''
 
* '''Occurrance''': ''If a note contained two home phone numbers, they would be "occurrance 0" and "occurrance 1". If "occurrance 1" was required, the function requires this to be specified. This value is optional, and if not specified, the function will default to using zero.''
 
|- valign="top"
 
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Examples
 
|style="background: #ecfeea; color: black; border: 1px solid black" | '''note(phone)'''<br>'''note(phone,home)'''<br>'''note(phone,home,1)'''<br>''Here are three sample notes expressions. In the image below, they have been used to create expression list columns, with each expression used shown in the column header. The note, with labels on show, is visible on the right hand end of the image. When comparing the note with the data returned by each expression, it should become apparent how each expression is working.''
 
[[image:Notes.png|thumb|left|500px|alt=note image|A note + expression columns (''click to enlarge)'']]
 
|}
 
<div style="text-align:right;">([[#top|Back to top)]]</div>
 
<br><br>
 
===Redundant Functions?===
 
Taken at face value, all of the functions in this section would appear to be a little on the redundant side, falling neatly into the "a long way for a shortcut" category. MEDIA CENTER could possibly rely on these functions internally, exalting their status to "highly useful" or "essential" even, but as this page is designed for end users, not MEDIA CENTER, end users will find these functions redundant, and they are included here in the name of completeness only.
 
====Field(...): Returns the value of a library field====
 
{| style="width: 100%; border: 1px solid black" align="top" border="1" cellpadding="3"
 
|- valign="top"
 
! scope="row" style="white-space:nowrap; background: #A8E4A0; color: black; border: 1px solid black;" width=100 | Field()
 
| style="background: #ecfeea; color: black; border: 1px solid black" width=1200 | Place the name of any library field inside this function, and it will return the contents of that library field for each file. Entering the field name inside square brackets as normal, without the function, returns the same data.
 
|- valign="top"
 
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Construction
 
| style="background: #ecfeea; color: black; border: 1px solid black" | '''Field(Field name to retrieve)'''
 
|- valign="top"
 
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Examples
 
|style="background: #ecfeea; color: black; border: 1px solid black" | '''field(duration)'''<br>''Returns the formatted duration value for each file. '''field(duration,0)''' would return the raw duration data. Simply entering [duration] or [duration,0] returns the same result.
 
|}
 
<div style="text-align:right;">([[#top|Back to top)]]</div>
 
====FilePath(...): Returns the path from a specified filename====
 
{| style="width: 100%; border: 1px solid black" align="top" border="1" cellpadding="3"
 
|- valign="top"
 
! scope="row" style="white-space:nowrap; background: #A8E4A0; color: black; border: 1px solid black;" width=100 | FilePath()
 
| style="background: #ecfeea; color: black; border: 1px solid black" width=1200 | This function will return the file path information from root to parent folder for all files in a list, or for any specified file. MEDIA CENTER has a [Filename (Path)] library field by default, which is probably easier to use or reference than this function.
 
|- valign="top"
 
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Construction
 
| style="background: #ecfeea; color: black; border: 1px solid black" | '''FilePath(Filename to check)'''
 
 
 
* Filename to check ''This is optional. If not specified, the function defaults to the current file.''
 
|- valign="top"
 
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Examples
 
|style="background: #ecfeea; color: black; border: 1px solid black" | '''filepath(C:\Music\File.mp3)'''<br>''The result here would be... "C:\Music"''
 
 
 
<br>'''filepath()'''<br>''Returns the filepath for each file in the list. The [filename (path)] field returns the same information.
 
|}
 
<div style="text-align:right;">([[#top|Back to top)]]</div>
 
====FileName(...): Returns the name from a specified filename====
 
{| style="width: 100%; border: 1px solid black" align="top" border="1" cellpadding="3"
 
|- valign="top"
 
! scope="row" style="white-space:nowrap; background: #A8E4A0; color: black; border: 1px solid black;" width=100 | FileName()
 
| style="background: #ecfeea; color: black; border: 1px solid black" width=1200 | This function will return the file name information for all files in a list, or for any specified file. MEDIA CENTER has a [Filename (Name)] library field by default, which is probably easier to use or reference than this function.
 
|- valign="top"
 
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Construction
 
| style="background: #ecfeea; color: black; border: 1px solid black" | '''FileName(Filename to check)'''
 
 
 
* Filename to check ''This is optional. If not specified, the function defaults to the current file.''
 
|- valign="top"
 
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Examples
 
|style="background: #ecfeea; color: black; border: 1px solid black" | '''filepath(C:\Music\File.mp3)'''<br>''The result here would be... "File.mp3"''
 
 
 
<br>'''filepath()'''<br>''Returns the file name for each file in the list. The [filename (Name)] field returns the same information.
 
|}
 
<div style="text-align:right;">([[#top|Back to top)]]</div>
 
====FileVolume(...): Returns the volume name from a specified filename====
 
{| style="width: 100%; border: 1px solid black" align="top" border="1" cellpadding="3"
 
|- valign="top"
 
! scope="row" style="white-space:nowrap; background: #A8E4A0; color: black; border: 1px solid black;" width=100 | FileVolume()
 
| style="background: #ecfeea; color: black; border: 1px solid black" width=1200 | This function will return the volume name information for all files in a list, or for any specified file. MEDIA CENTER has a [Volume Name] library field by default, which is probably easier to use or reference than this function.
 
|- valign="top"
 
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Construction
 
| style="background: #ecfeea; color: black; border: 1px solid black" | '''FileVolume(Filename to check)'''
 
 
 
* Filename to check ''This is optional. If not specified, the function defaults to the current file.''
 
|- valign="top"
 
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Examples
 
|style="background: #ecfeea; color: black; border: 1px solid black" | '''filevolume(C:\Music\File.mp3)'''<br>''The result here would be... "C:"''
 
 
 
<br>'''filevolume()'''<br>''Returns the file name for each file in the list. The [Volume Name] field returns the same information.
 
|}
 
<div style="text-align:right;">([[#top|Back to top)]]</div>
 
====AlbumKey(...): Returns a unique album key for a file====
 
{| style="width: 100%; border: 1px solid black" align="top" border="1" cellpadding="3"
 
|- valign="top"
 
! scope="row" style="white-space:nowrap; background: #A8E4A0; color: black; border: 1px solid black;" width=100 | AlbumKey()
 
| style="background: #ecfeea; color: black; border: 1px solid black" width=1200 | Testing reveals that this function simply returns an "'''[album artist (auto)] - [album]'''" string for each file. If two different albums happen to have the same [album&nbsp;artist&nbsp;(auto)] and [album] data, their respective AlbumKey() will not be unique.
 
|- valign="top"
 
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Construction
 
| style="background: #ecfeea; color: black; border: 1px solid black" | '''AlbumKey()'''
 
|- valign="top"
 
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Examples
 
|style="background: #ecfeea; color: black; border: 1px solid black" | '''AlbumKey()'''<br>''Create a new expression column in a list using this function and the result will be a column populated with the [album artist (auto)] - [album] data for each file.
 
|}
 
<div style="text-align:right;">([[#top|Back to top)]]</div>
 
====AlbumArtist(...): Returns the calculated album artist for a file====
 
{| style="width: 100%; border: 1px solid black" align="top" border="1" cellpadding="3"
 
|- valign="top"
 
! scope="row" style="white-space:nowrap; background: #A8E4A0; color: black; border: 1px solid black;" width=100 | AlbumArtist()
 
| style="background: #ecfeea; color: black; border: 1px solid black" width=1200 | This function simply returns the "'''[album artist (auto)]'''" data for each file.
 
|- valign="top"
 
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Construction
 
| style="background: #ecfeea; color: black; border: 1px solid black" | '''AlbumArtist()'''
 
|- valign="top"
 
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Examples
 
|style="background: #ecfeea; color: black; border: 1px solid black" | '''AlbumArtist()'''<br>''Create a new expression column in a list using this function and the result will be a column populated with the [album artist (auto)] data for each file.
 
|}
 
<div style="text-align:right;">([[#top|Back to top)]]</div>
 
====AlbumType(...): Returns the album type for a file====
 
{| style="width: 100%; border: 1px solid black" align="top" border="1" cellpadding="3"
 
|- valign="top"
 
! scope="row" style="white-space:nowrap; background: #A8E4A0; color: black; border: 1px solid black;" width=100 | AlbumType()
 
| style="background: #ecfeea; color: black; border: 1px solid black" width=1200 | This function simply returns the "'''[album type]'''" for each file. [album type] is a default MEDIA CENTER library field that informs the user of an album's status in the library, such as "Single artist (complete)" or "Multiple artists (incomplete)"
 
|- valign="top"
 
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Construction
 
| style="background: #ecfeea; color: black; border: 1px solid black" | '''AlbumType()'''
 
|- valign="top"
 
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Examples
 
|style="background: #ecfeea; color: black; border: 1px solid black" | '''AlbumType()'''<br>''Create a new expression column in a list using this function and the result will be a column populated with the [album type] data for each file. The [album type] library field will work just as well, and return the same information.
 
|}
 
<div style="text-align:right;">([[#top|Back to top)]]</div>
 
====Size(...): Returns the size of a file in a media type independent manner====
 
{| style="width: 100%; border: 1px solid black" align="top" border="1" cellpadding="3"
 
|- valign="top"
 
! scope="row" style="white-space:nowrap; background: #A8E4A0; color: black; border: 1px solid black;" width=100 | Size()
 
| style="background: #ecfeea; color: black; border: 1px solid black" width=1200 | Dependent on media type, this function returns the following information:
 
 
 
* Audio: ''Duration''
 
* Video: ''Duration''
 
* Image: ''Dimensions''
 
* Data: ''No information returned.''
 
 
 
|- valign="top"
 
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Construction
 
| style="background: #ecfeea; color: black; border: 1px solid black" | '''Size()'''
 
|- valign="top"
 
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Examples
 
|style="background: #ecfeea; color: black; border: 1px solid black" | '''Size()'''<br>''Create a new expression column in a list using this function and the result will be a column populated with media type dependent data for each file as listed in the function description above.
 
|}
 
<div style="text-align:right;">([[#top|Back to top)]]</div>
 
====TrackNumber(...): Returns the track # of a file====
 
{| style="width: 100%; border: 1px solid black" align="top" border="1" cellpadding="3"
 
|- valign="top"
 
! scope="row" style="white-space:nowrap; background: #A8E4A0; color: black; border: 1px solid black;" width=100 | TrackNumber()
 
| style="background: #ecfeea; color: black; border: 1px solid black" width=1200 | This function simply returns the track # of a file. If a file has no track # assigned, the function returns zero.<br>This function has no real use and is actually flagged as "For internal use only", so, not one for end users, and again, only included here for the sake of completeness.
 
|- valign="top"
 
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Construction
 
| style="background: #ecfeea; color: black; border: 1px solid black" | '''TrackNumber()'''
 
|- valign="top"
 
! scope="row" style="background: #A8E4A0; color: black; border: 1px solid black;" | Examples
 
|style="background: #ecfeea; color: black; border: 1px solid black" | '''TrackNumber()'''<br>''Create a new expression column in a list using this function and the result will be a column populated with the track # information for each file.
 
|}
 
<div style="text-align:right;">([[#top|Back to top)]]</div>
 
 
 
[[User:Marko|marko]] 13:20, 7 October 2010 (CDT)
 
 
 
[[Category:Frequently_Asked_Questions]]
 

Latest revision as of 01:44, 30 June 2019

Media Center provides a simple programming language that enhances and enriches its overall user interface and usability. This language, commonly called the expression language, is simple to learn, simple to use, and can greatly enhance your experience using Media Center.

Expressions are ubiquitous throughout Media Center, used in areas such as:

  • The categories in a view
  • File list expression columns
  • Theater View
  • Customized view headers, grouping and sort criteria
  • The library field manager (fields with data type Calculated data)
  • File and folder location definitions
  • Auto-import rules
  • Custom DLNA titles
  • The player's display
  • Captions and thumbnail text
  • The link manager (expressions help format link URLs)
  • Rename, Move, & Copy tool
  • Tag assignment
  • Complex search queries

An expression is a mixture of ordinary text, pre-defined functions, and a few reserved characters and constructs that have special meaning. An expression is evaluated by Media Center's expression engine and textual output is produced. This output is then used by Media Center to customize the user interface and affect its method of operation.

The Anatomy of an Expression

As mentioned above, an expression is a mixture of text and function calls (and some reserved stuff described shortly). The simplest expression would be some basic, literal text, such as A good movie. The expression engine evaluates this expression, finds nothing special, and then outputs the result: A good movie. Simple.

But simple text only has so much utility. The ability to transform or generate content is much more interesting and useful. And this is when functions are employed. Media Center provides many functions, which when called, produce some output. Most functions require some form of input, called arguments, and most functions generate output. By supplying a function with various arguments, the function will return some output value which is just more text. And this output text can be the used by other functions, and so on. Each function has a unique name, and calling upon a function to do some work requires little more that using its name anywhere in the expression.

A function call looks like this:

functionname(argument 1, argument 2, ...)

The syntax of the function call is the function's case-insensitive name, immediately followed by an opening parenthesis character, one or more comma-separated arguments, and a closing parenthesis character. Whitespace after the commas is optional, but helps readability and formatting. And each argument itself is also just an expression. And some arguments are optional. If an argument is optional, it can be omitted and its default value will be used. If the argument is omitted, a comma-separator will still be required if additional arguments follow. The following example uses the FixCase() function to change its input to Title Case:

fixcase(A good movie)

The result is A Good Movie.

A slightly more complex expression example consists of both text and a nested function call:

Wow! fixcase(replace(A good movie, good, great))

Inner functions are called before outer functions, so the Replace() function is call first:

replace(A good movie, good, great)

and its output is then supplied as the input to the FixCase() function. Replace() does its work substituting good with great, and returns A great movie. This output is then supplied as the argument to FixCase() which sees only the text A great movie (it knows nothing about how it was produced). So the function call:

fixcase(A great movie)

in turn outputs A Great Movie. Now that the functions have produced their output, the final output, including the literal Wow! leading text is

Wow! A Great Movie

Fields

The expression examples thus far have been limited to static literal text. Expressions have much more utility when they use data from other sources, such as a file's metadata. Media Center maintains this metadata in its defined fields. This data is accessed using the Field() function, and its first argument is the case-insensitive name of the field to be accessed. For example, the function call field(album) will return the current* file's value for the album field (* more will be said later about the current file). If the album field contained the value After Hours, the expression:

fixcase(field(album), 3)

would produce AFTER HOURS. First field(album) is evaluated, returning After Hours. The FixCase() function is supplied with this output as its first argument, and its second argument is 3, which happens to specify that it should perform upper-casing.

Because fields are so frequently used in expressions, an abbreviated form called square bracket notation exists for accessing their values. This makes it easier to both read and write expressions. Nonetheless, both forms are equivalent. The abbreviated form is simple: immediately surround the field's name with opening and closing square brackets, for example, [album]. The previous example is now written more simply as:

fixcase([album], 3)

Field Values

For the sake of simplicity and clarity, the section above glossed over an important detail regarding how Media Center outputs field values. Recall that Field() is the function used to return the value of a specified field. But Field() also has a second argument that indicates the format of the value that it returns. Because field values are used in a variety of situations, the Field() function can produce output suitably formatted for the requirements. There are two forms of output: one is a nice, friendly human-readable format suitable for use in views or other display locations; the other is a raw format which returns the representation stored internally by Media Center which is useful when uninterpreted values are necessary.

By default, Media Center always outputs the friendly format, so expressions sometimes need to take this into account and chose the format accordingly.

Not used earlier because it is optional, the second argument to the Field() function selects the mode of output: the value 0 selects the raw mode, and the default value of 1 selects the friendly mode. Here are two examples using the date field, the first one outputs the date value in raw format, the second in the friendly format:

field(date, 0)
field(date, 1)

Field Values: Empty, 0, and 1

The Media Center expression language does not strongly differentiate between the numeric value zero 0 and emptiness for numeric field types Integer and Decimal. And in some cases, the numeric value of 1 is treated similarly to the empty value.

When a value of 0 is entered as a numeric field's value, the raw value will be shown as 0, but the display format (as in the file list) will be shown as empty. The empty display allows for less visual noise in the user interface, since a column full of 0 values is not usually helpful. In fact, if you attempt to set a numeric field's value to 0 in the file list, it will immediately be displayed as empty.

Generally this difference is unimportant, except when testing numeric values with IsEmpty() or IsEqual(). It is easy to be fooled when testing such a value if the value shown in a file list is empty. The values shown in the Tag Action Window will reveal the actual raw value, as will an expression column using the field's raw format.

Another consideration for integer fields is that when sorting, a 1 value can sometimes sort indistinguishably from an empty value. The Integer type disc # field is typically empty when an album consists of only one disc, and as such, Media Center will sort the disc # values of empty (0) and 1 identically.

The friendly output of a field can differ, depending on context. For example, in a file list, and empty field will be shown as blank, but in the Rename, Move & Copy tool, it will be output as Unknown Disc # (this ensures no blank values are generated as path components). To test such a field, always use and test against the raw format, and then expressions will be context agnostic.

Field Assignment

The output of an expression can be used to assign a value to a tag. This is accomplished by preceding the expression with an = character. The = character causes the tagging engine to invoke the expression evaluator first, and then to use its output as the value to assign to the field.

Field Assignment with Expression.png

Without the prepended = character, the literal expression text itself and not its evaluated value would be stored in the tag. The expression can refer to the field's own value to modify itself, and this offers a convenient way to perform complex transformations on field values. For example, the assignment expression

=removeleft([name], 4)

entered into an edit cell for the name field would remove four characters from the left of the name field's current value. An assignment expression can be entered into the Tag Action Window, or by using inline editing in the file list or a pane entry. The image on the right shows in-place field assignment.

Note: Undo is supported, reverting each tag to its value prior to the assignment. Redo is also supported, reapplying the most recent Undo.

Expression Language Syntax

Now that the basics have been covered, the more rigorous rules of the expression language syntax can be described.

  • An expression is any sequence of literal text and any number of function calls.
  • Expressions are read and evaluated left to right. Literal text is output unmodified, function calls are evaluated and their return values output.
  • Fields designated using square bracket notation are expanded into the equivalent Field() function call.
  • Nested function calls are evaluated from the innermost function to outermost function, and again, left to right when one function follows another.
  • A function is evaluated and its returned value contextually replaces the function call in the expression
  • Within a function's argument list, whitespace is ignored before and after commas, after an opening parenthesis, and before a closing parenthesis.
  • The forward-slash escape character / disables the special meaning of the character that follows it.
  • The escape sequence /# followed by #/ escapes everything inside.
  • To use a literal parenthesis, comma, or whitespace inside of function argument lists, escape them. Whitespace within an argument's value is literal and does not need to be escaped when it is surrounded by other non-whitespace text.
  • An expression may be split into multiple lines, but when it does not satisfy the conditions above regarding whitespace around function parenthesis and commas, use a forward-slash escape as the last character before the newline. Extraneous newlines in the expression editor will produce a trailing ellipsis (...) in the output.

How Expressions Are Evaluated

Expressions are evaluated in the context where they are used. For example, an expression column in a file list is evaluated relative to those files in the file list. And the general flow is that for each file in the list, the expression is evaluated and produces output. The expression only has access to the fields available for the file currently being evaluated. This is important to remember, so it bears repeating. One file after another, an expression is evaluated against that single file, its output is produced and stored away for use later, and then the result of that evaluation is entirely forgotten before the next file is evaluated. This means, the expression evaluator cannot use the results from one file's evaluated expression with the results of another file's evaluation.

Expressions and Locales

Media Center will respect the Windows locale setting for output values produced by certain functions, and within the values of certain fields. This is important to consider when writing expressions that consume such values. Under most circumstances, such values cause no harm. However special care must be taken with functions that require the use of period as the decimal point. One such function is Math(), which always uses period as the decimal point. If your locale uses some other character such as comma, these characters will have to be converted into periods before the critical function is called. Handling this problem is not difficult. Before passing to Math() any floating point number, use Replace() first when necessary to convert the locale's decimal character into a period. Fields that cause problems are any fields that produce floating-point values, such as any Date type field in raw format (e.g. [date,0], [last played,0], [date modified,0], and [date imported,0]), or any textual field that contains floating-point values that will be used for various calculations (e.g. any of the Dynamic Range variants). Certain functions such as Now() and ConvertTime() also return localized floating-point values. Consider also that the expression parser uses comma as the argument separator. Any literal numeric values specified as a function argument must have any embedded commas escaped.

A Complex Expression Example

Expression Editor.png

Here is a more complex expression example that illustrates the various rules discussed above regarding expressions:

if( IsEmpty( [Disc #] ),
Disc number is empty,
Delimit(
field(disc #) ,
/) ,
DISC /(
)
)

The expression demonstrates that

  • whitespace before and after commas or opening and closing parenthesis is ignored
  • expressions can be safely split into multiple lines using the whitespace rules just mentioned
  • function and field names are case insensitive
  • forward slash is used and required to escape parenthesis (see inside the Delimit() function)
  • whitespace does not require escapement when surrounded by other characters (see after the C in DISC)
  • literal text is output unmodified (Disc number is empty)
  • functions can be nested (Both IsEmpty() and Delimit() are nested within the If() function, and the Field() function is nested within Delimit()

When the expression is run, files that have no disc number will produce Disc number is empty, and files that have, say, a disc number value of 3 will produce DISC (3).

Functions

Functions enable you to transform or generate content automatically. For background information on how functions are used in expressions, refer to The Anatomy of an Expression section above.

This section describes all the various functions provided by Media Center's Expression Language.

Function Arguments

As discussed above, a function call consists of the function's case-insensitive name, immediately followed by an opening parenthesis character, one or more comma-separated arguments, and a closing parenthesis character:

functionname(argument 1, argument 2, ...)

Functions may have one or more arguments. In some cases, these arguments are optional, and will automatically use a default value if omitted. For example, these two expressions are equivalent because the mode argument for IsEmpty() is optional and defaults to 0:

isempty([comment], 0)
isempty([comment])

In this case, a comma-separator will still be required if additional arguments follow the optional one. Whitespace after the commas is also optional, but helps readability and formatting. However, if any extra arguments are included in a function call which are not valid for that function, they are dropped and omitted from output. This is of particular importance when using string-manipulation functions on text. If the text you enter contains any commas, these must be escaped or the expression engine will consider text after the comma to be additional arguments.

The arguments themselves are also just expressions, and you can nest multiple functions to achieve complex logic:

if(isequal([artist], [album], 1), Eponymous, [album])

Nested function calls are always treated as a single argument when used as the input to another function (so that commas in the output of one function do not need to be escaped to be used as input in another function). This includes fields, since they are expanded to the equivalent Field() function call.

Please Note: In some cases below, such as with Unswap(), we have ignored this detail in order to simplify the examples. If you enter any text manually into a function, all commas must be escaped in order to achieve the correct result. This detail is unimportant in most real-world usages, however, because you will typically use either field values or the output of other functions as the arguments in your expressions. However, if you need to include commas in a string literal argument to a function, you need to escape every one, or block escape the entire argument.

Function Index

Accessing and Storing Functions

Conditional Functions

Test and Comparison Functions

Formatting Functions

String Manipulation Functions

  • Clean(…): Clean a string to be used for various operations
  • FixCase(…): Changes the case of a given string
  • FixSpacing(…): Intelligently splits adjacent camel-cased words
  • Hexify(…): Hexifies a string to make it suitable for web usage
  • Left(…): Retrieves a specified number of characters from the left of a string
  • Length(…): Returns the number of characters in a string
  • Mid(…): Retrieves specified characters from a string
  • Regex(…): Regular expression pattern matching and capture
  • RemoveCharacters(…): Removes a list of characters from a string
  • RemoveLeft(…): Trims characters from the beginning of a string
  • RemoveRight(…): Trims characters from the end of a string
  • Replace(…): Replace or remove a string segment
  • Right(…): Retrieves a specified number of characters from the right of a string
  • Swap(…): Takes Firstname Lastname and swaps to Lastname, Firstname.
  • Unswap(…): Takes Lastname, Firstname and reverses it to Firstname Lastname.

List Manipulation Functions

Date and Time Functions

  • ConvertDate(…): Converts a human-readable date to the internal format required for use in date fields
  • FormatDate(…): Formats a date value in a specified manner
  • Now(…): Retrieve and display the system date

File Path and Identifier Functions

Grouping Functions

  • GroupCount(…): Counts the members of a specified group (in a category or field).
  • GroupSummary(…): Smartly summarizes the members of a specified group (mode, mean, min, max, etc as is most logical for that grouping).

Miscellaneous Functions

Data Types

It was mentioned already that the Media Center expression language is primarily a textual language - it consumes and produces text. Nonetheless, certain areas of Media Center are influenced by the type of data used or presented, and sometimes it is useful or necessary to coerce expression output into one data type or another. Each Media Center field is defined to be of a certain data type, listed in the Field Data Types table. These types influence how values are output, sorted, and interpreted on input. And expressions always output data of type String. By coercing the data type of an expression, output formatting and sorting can be controlled in various ways.

Data types are forced by appending to an expression the string:

&datatype=[type]

where type is one of the following values:

listA list of strings, separated by semicolons
stringSorts as strings (with smart number handling)
numberSorts values as numbers (decimal or integer)
integerSorts values as integers
pathSorts using a smart filename compare style
monthSorts string month names (i.e. January, February, etc.)

Calculated Fields and Search

Media Center's Search Language supports some simple numeric comparison operators. Because expressions always evaluate as a String type, these operators would be unavailable for use in a search query to compare numeric values from a calculated expression field. In order to use the numeric comparison operators, a calculated expression field can be cast into one of the numeric types. In your numeric calculated fields, to allow the use Search's numeric comparison operators, add either of the casts:

&datatype=[integer]
&datatype=[number]

to the end of the field's calculated expression.

Lists and Trees

Datatype List.png

The list of output in view categories and pane columns can be modified by forcing the data type to a List type. Two things happen when the data type is List: The values within a List type are split into their individual (semicolon-separated) list items The backslash character takes on a special meaning and becomes another form of separator that creates tree-like hierarchies, collapsible in panes columns and creates drill-down categories in any category view type (Standard View > Categories, Theater View, DLNA, Gizmo/WebGizmo). Forcing an expression's type to list causes this list item separation and hierarchy generation. Alternatively, forcing a List type to string defeats this. Add the cast:

&datatype=[list]

to the end of an expression to force an expression's output to be considered as a List type. Conversely, a List type may be forced into a String type by adding the cast:

&datatype=[string]

to the end of an expression.

Sort Order

Datatype Month.png

Normally strings are sorted ASCII-betically with some smart numeric sorting. But this form of sort may not always be desired.

Sorting by Month

Generally it is more useful to see month names sorting such that January sorts before April, instead of alphabetically where April would sort before January. Forcing an expression's type to Month forces string month values to be treated instead as their equivalent numerical month numbers. For example, the first month January and the third month March sort before the fourth month April. Add the cast:

&datatype=[month]

to the end of an expression to force an expression's output to be sorted by numeric month values.

Sorting by Path

Path data types sort using smart filename comparisons.

XXX: Note: This section is incomplete. I cannot distingish any difference between using a datatype of path vs. string. It seems path sort order is always engaged.

Add the cast:

&datatype=[path]

to the end of an expression to force an expression's output to be smart-sorted by path components.

Expressions and Search

The expression language is fully available to the search query engine (Search, Set rules for file display, etc.). This allows creation of more complex search queries than would otherwise be possible. An expression-based search query is any valid expression that produces a zero or non-zero numeric output. The syntax of the query is:

[=expression]=numval

where expression is any valid expression, and numval is the expected numeric output produced by the expression. The expression is evaluated against the current list of available files and the expression output numerically compared against numval. All files for which the comparison is true are returned as part of the file list produced by the query and all files that fail the comparison are winnowed from the file list.

The following example illustrates an expression-based search query:

[=ismissing([filename (path)]\Folder.jpg)]=1

The IsMissing() function is run using the file name argument [filename (path)] appended by \Folder.jpg, and returns a Boolean value 1 for files that are missing, and this 1 is compared against the value numval. All these files where there was a successful comparison are returned in the file list, and all those for which the expression produced 0 are filtered from the file list. By inverting the comparison and using a 0 numval, the set of files remaining in the file list would be those that did not match.

HTML Font Properties

The expression language recognizes a limited set of HTML font properties and attributes. These can be used to set font styles in most text drawing areas, such as captions, thumbnail text and in the configuration of Theater View. HTML tags are used by surrounding the desired content with an opening and closing tag, in the form of:

<tag>desired content<//tag>

The supported HTML tags are:

<b>Bold
<i>Italics
<u>Underline
<font>Font properties (see attributes below)

The font tag supports the following attributes:

alphaSets alpha-blending percentage (0 - 100)
colorSets the foreground color (RGB hex values from 00 to ff in the form of rrggbb)
bgcolorSets the background color (same values as color)
faceSets the font face (a font name)
sizeSets the font size (a percentage scaling value)

Any combination of HTML tags and font attributes can be used. An HTML tag must have an opening and closing tag. Nesting is allowed, but be sure to properly balance like opening and closing tags. Attribute values must be double quoted. The closing tag's forward slash requires escapement with an extra forward slash. The following examples illustrate using HTML font properties:

<i>This is in italics<//i>
<i><b>And this is bold and italic<//b><//i>
<b>The<font color="ff0000" size="80" alpha="50"> Great <//font>Gatsby<//b>

Expression Editors

There are a couple of variations of dialog or edit field used to enter expressions. Some allow multi-line expressions, while others are single line, but can be expanded to multi-line editors. Unfortunately, some single-line editors flatten multi-line expressions into a single line, replacing the newlines with spaces.

Acknowledgements

A big tip of hat to marko who tackled the enormous challenge of documenting the MC Expression Language in detail. His work was instrumental and through which has brought clarity and great assistance to Media Center users worldwide.

Also, a huge thanks to user MrC who built the amazing and long-lived previous version of this page, upon which this is still heavily based.

The current caretaker of this documentation is forever in their debts.