reduce

array →
reduce(
    operation: expression,
    initial?: any
) → any

Combines array elements in source order by repeatedly evaluating an expression against the accumulated value and current element.

Parameters

Name	Type	Required	Description
operation	expression	Yes	Specifies the expression evaluated against each accumulated-value/current-element tuple.
initial	any	No	Specifies the initial accumulated value and the result returned for an empty array.

Argument evaluation

Visits the array supplied to this reduce call in source order, starting with the second element when initial is omitted and with the first when initial is supplied.

• operation: Evaluated once per visited element with T(accumulator, current item) as input and argument context; $0 is the accumulated value and $1 the current item. Tuple-valued items remain nested in their position.
• initial: Evaluated once before accumulation, using the incoming collection as its context.

Behavior

The combining expression receives a two-element tuple: $0 is the accumulated value and $1 is the current element. Without initial, the first element becomes the accumulated value and an empty array returns null. With initial, evaluation starts by combining it with the first element, and an empty array returns the initial value unchanged. f~ invokes accumulator

f(current item); ~f invokes current item

f(accumulator). Existing complete expressions and the normalization of an explicitly supplied leading $0 are preserved and are not deprecated.

Examples

{1, 2, 3, 4} | reduce(add($0, $1)) → 10
{1, 2, 3} | reduce(add($0, $1), 10) → 16
{20, 3, 2} | reduce(subtract~) → 15

Kind: Accumulator
Scope: array
Aliases: reduce