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reduce() Function


reduce( function, initial, list, context )

Calls a rule or function for each item in a list, passing the result of each call to the next one, and returns the value of the last computation.


Keyword Type Description


Rule or Function Reference

Rule or expression function.


Any Type

The accumulator's initial value.


Any Type

Array of elements that the function iterates through.


Any Type Array

Variable number of parameters passed directly into each function evaluation.


Any Type

Usage considerations

Referencing expressions and rules

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

The initial accumulator value is given by initial.

Using rules or functions with multiple arguments

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

Understanding results

Null lists return a null list without executing the function.

Returns a scalar value if the function called returns a scalar, and returns a list if the function called returns a list.

Limitations and alternatives

Best used when the computation of each operation needs to use the result from the previous operation such as when the result of each operation is an array that should be appended to each other in order. The result from the previous operation is then passed to the subsequent operation as the parameter initial.

a!forEach() cannot be used within rules used in this function.


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

reduce(fn!sum, 0, {1, 2, 3}) returns 6

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
Process Reports Incompatible

You cannot use this function to configure a process report.

Process Events Incompatible

You cannot use this function to configure a process event node, such as a start event or timer event.

reduce() Function