fold()
Reduce the array to a single, accumulated value by applying a function to each element. Iterates through elements from left to right. Uses a provided seed as the initial value.
Description
The fold() method iterates through each element in an array to perform
a rolling operation. For example, you can use fold() to calculate a
rolling sum, concatenate elements, or perform complex transformations.
fold() calls a reducer callback function on each element of the array from
left to right. 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:
-
fold()andfoldRight()accept an initial seed value and use it as the initial accumulator.reduce()andreduceRight()use the array’s first element as the initial accumulator. -
fold()andreduce()iterate through the array’s elements from left to right.foldRight()andreduceRight()iterate through the array’s elements from right to left.
Parameters
| Parameter | Type | Required | Description |
|---|---|---|---|
seed |
Yes |
Initial accumulator value provided to the reducer function. |
|
reducer |
Yes |
Anonymous FQL function to call on each array element. |
Return value
| Type | Description |
|---|---|
Result of the last reducer function call. For an empty array, the seed is returned. |
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