`array.foldRight()`

This method operates on an array. You typically fetch documents from a collection as a set, not an Array. For the equivalent Set method, see set instance methods.

For differences between Sets and Arrays, see Sets vs. Arrays.

Reduce the Array to a single, accumulated value by applying a function to each element. Iterates through elements from right to left. Uses a provided seed as the initial value.

Signature

foldRight(seed: B, reducer: (B, A) => B) => B

Description

The foldRight() method iterates through each element in an Array to perform a rolling operation. For example, you can use foldRight() to calculate a rolling sum, concatenate elements, or perform complex transformations.

foldRight() calls a reducer callback function on each element of the Array from right to left. The reducer function takes two arguments:

The accumulator that holds the running result from previous iterations. For the first iteration, a seed value serves as the initial accumulator.
The current element’s value from the Array.

The method returns the result of the last iteration. The calling Array isn’t changed.

Fold family methods

FQL supports several methods for folds, which iteratively reduce an Array to a single value. These methods include:

The methods are similar but have the following differences:

array.fold() and array.foldRight() accept an initial seed value and use it as the initial accumulator. array.reduce() and array.reduceRight() use the array’s first element as the initial accumulator.
array.fold() and array.reduce() iterate through the Array’s elements from left to right. array.foldRight() and array.reduceRight() iterate through the Array’s elements from right to left.

Parameters

Parameter	Type	Required	Description
seed	Any	Yes	Initial accumulator value provided to the reducer function.
reducer	Function	Yes	Anonymous FQL function to call on each Array element.

Parameter

Type

Required

Description

seed

Any

Yes

Initial accumulator value provided to the reducer function.

reducer

Function

Yes

Anonymous FQL function to call on each Array element.

reducer parameters:

Parameter	Type	Required	Description
accumulator	Any	Yes	Value returned by the previous reducer function call. On the first call, seed is passed as the accumulator.
current	Any	Yes	The current element’s value.

Parameter

Type

Required

Description

accumulator

Any

Yes

Value returned by the previous reducer function call. On the first call, seed is passed as the accumulator.

current

Any

Yes

The current element’s value.

Return value

Type	Description
Any	Result of the last reducer function call. For an empty Array, the seed is returned.

Examples

let iter = [1, 2, 3]
iter.foldRight(100, (value, elem) => value + elem)

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