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apply() Function

Tip:  Check out the new looping function, a!forEach(). It does everything apply() does but with easier syntax, better null handling, and support for interface components.


apply( function, list, context )

Calls a rule or function for each item in a list, and provides any contexts specified.

See also:


Keyword Type Description


Rule or Function Reference

Rule or expression function.


Any Type Array

List of elements that function iterates through.


Any Type Array

Variable number of parameters passed directly into each function evaluation.


Any Type Array

Usage considerations

Referencing expressions and rules

Use fn!functionName to reference an expression function and rule!ruleName to reference a rule.

Using rules or functions with multiple arguments

To use rules or functions that take more than one argument, use the merge() function. For example, given a rule g(x, y), apply(rule!g, merge({a, b, c}, {d, e, f})) returns {g(a, d), g(b, e), g(c, f)}.

Understanding results

Null lists return a null list without executing the function.

The result of each operation is appended to each other in the same order as their corresponding item in the input list. If the result of each operation is an array, apply() returns a two-dimensional array which can then be used for further computation. When the two-dimensional array is saved into a process variable, a node input or a custom data type, the array is flattened to a one-dimensional array. Local variables, however, can store the two-dimensional array without flattening it.

Flattening data

If you save the nested arrays into a process variable for multiple values, the nested function is flattened. Keep in mind that casting to a flattened array only happens when saving into a process variable, node input, custom data type, or custom data type field.

To avoid having the nested function flatten, you can use the output of the apply() function as the input for a merge() function.

Alternatives when working with local data

apply() cannot be used with rules or functions that store local data. This means any local variable that can be saved into, such as variables created using load() or a!localVariables() without using the "refreshAlways" configuration, cannot be created. Additionally, a!forEach() and some components cannot be used. In these cases, apply() will return an error. In these cases, use a!forEach() or a!applyComponents() instead of apply().


Given a function h(x, y), apply(fn!h, {a, b, c}, v) returns {h(a, v), h(b, v) ,h(c, v)}

apply(fn!sum,{-1,2,3},2) returns 1, 4, 5

Feature compatibility

The table below lists this function's compatibility with various features in Appian.
Feature Compatibility Note
Portals Compatible
Offline Mobile Compatible
Sync-Time Custom Record Fields Compatible

Can be used to create a custom record field that only evaluates at sync time.

Real-Time Custom Record Fields Incompatible

Custom record fields that evaluate in real time must be configured using one or more Custom Field functions.

Process Reports Incompatible

Cannot be used to configure a process report.

Process Events Incompatible

Cannot be used to configure a process event node, such as a start event or timer event.

Open in Github Built: Thu, Jun 13, 2024 (05:06:58 PM)

apply() Function