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.

Parameters

Keyword	Type	Description
function	Rule or Function Reference	Rule or expression function.
initial	Any Type	The accumulator's initial value.
list	Any Type	Array of elements that the function iterates through.
context	Any Type Array	Variable number of parameters passed directly into each function evaluation.

Returns

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.

Examples

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.