Conditional Functions

From JRiverWiki
Revision as of 15:59, 25 January 2016 by Glynor (talk | contribs) (FirstNotEmpty(…))

(diff) ← Older revision | Latest revision (diff) | Newer revision → (diff)
Jump to: navigation, search

The functions in this section test one or more arguments to produce either a true or false outcome, and execute specific actions depending upon that result.

The expression language does not directly support AND, OR, and XOR operations. However, these can be easily emulated using any of several techniques. See: Boolean Operations.

The NOT operator ! (exclamation point) may be used in a conditional to invert the sense of the conditional test. Inverting the sense of a test can make reading expressions easier, or support better IfElse() sequences.


Conditional if-else evaluator.
Description If(test expression, true expression, false expression)

The If() function is used to evaluate a test expression, and will output the result of the true expression or false expression, depending upon the evaluation result. The test expression is expected to return a 0 (false value) or a non-zero (true value). Nesting is allowed. If the test expression is preceded by the NOT operator (!, an exclamation point), the sense of the test is inverted. Non-zero values are inverted to 0, and 0 is inverted to 1.

Examples if(isequal([artist], bob dylan, 1), Genius, Mediocre)
Outputs Genius when artist is (case insensitive) Bob Dylan and Mediocre otherwise.

if(isequal([artist], bob dylan, 1), Genius, if(isequal([album], Joshua Tree, 8), Great Album, Mediocre))

This nested If() expression expands on the previous example, by first evaluating if the artist is Bob Dylan, and outputs Genius if true. When the artist is not Bob Dylan, the album is then tested to see if it is Joshua Tree, and if so outputs Great Album, otherwise outputs Mediocre.

if(!isempty([comment]), regex([comment], /#^(\\S+\\s+\\S+\\s+\\S+)#/, 1), *No Comment)

Outputs the first three words of the comment field; otherwise, outputs *No Comment. By using the NOT operator, the sense of the conditional is inverted so that the more interesting case is moved ahead of the more mundane case.


Conditional if-elseif evaluator.
Description IfElse(test1, action1, test2, action2, test3, action3, …)

The IfElse() conditional provides a convenient mechanism for shortening and more clearly expressing nested conditionals into an alternating sequence of tests and actions. One or more test/action pairs may be specified.

For example, consider a nested sequence of If() tests such as the following pseudo-code:

if (test1)
else if (test2)
else if (test3)

The IfElse() statement may be used to more cleanly express the flow of expression by removing the superfluous internal If() statements, converting the clumsy expression:

if(test1, action1, if(test2, action2, if(test3, action3)))

into the more elegant:

ifelse(test1, action1, test2, action2, test3, action3)

If any of the test expressions test1, etc. are preceded by the NOT operator (!, an exclamation point), the sense of that test is inverted. Non-zero values are inverted to 0, and 0 is inverted to 1.

Examples ifelse(isequal([media type], Audio), Le Tunes, isequal([media type], Video), Flix)
If media type is audio, outputs Le Tunes, else if media type is video, outputs Flix.

ifelse(isequal([artist], Bob Dylan), Genius, isequal([album], Joshua Tree, 8), Great Album, 1, Mediocre)

This example, implements the nested if statements from the If() section above, first testing if the artist is Bob Dylan, and if true, outputs Genius, otherwise evaluates the second test to determine if the album is Joshua Tree, and if true, outputs Great Album, otherwise, performs a final test, in this case a degenerate test of 1 (and 1 is always true), thus outputting the value Mediocre.


Returns the first non-empty argument.
Description FirstNotEmpty(value1, value2, …)

The FirstNotEmpty() function acts as a conditional by returning the first argument from value1, value2, ... that is not empty. Two or more arguments may be used, and the first non-empty argument is returned. With two arguments, is is functionally equivalent to the sequence such as if(!isempty(value1), value1, value2). With more than two arguments, FirstNotEmpty() avoids long nested If() sequences that simply test for emptiness.

Examples firstnotempty([media sub type], Misc Video)
Returns the value in media sub type if it is not empty, otherwise returns Music Video.

firstnotempty([series], [name], Tag your Videos!)

Returns the first non-empty value from the fields series or name, and if both are empty, returns the reminder to Tag your Videos!.