array.reduce()
|
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 an Array to a single, accumulated value by applying a function to each element. Iterates through elements from left to right. Uses the first element as the initial value.
Description
The reduce() method iterates through each element in an Array to perform
a rolling operation. For example, you can use reduce() to calculate a
rolling sum, concatenate elements, or perform complex transformations.
reduce() 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. The first element in the Array 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()andarray.foldRight()accept an initial seed value and use it as the initial accumulator.array.reduce()andarray.reduceRight()use the array’s first element as the initial accumulator. -
array.fold()andarray.reduce()iterate through the Array’s elements from left to right.array.foldRight()andarray.reduceRight()iterate through the Array’s elements from right to left.
Parameters
| Parameter | Type | Required | Description |
|---|---|---|---|
reducer |
Yes |
Anonymous FQL function to call on each Array element. |
Examples
Reduce the Array elements to a single value:
["A", "B", "C"].reduce((prev, cur) => prev + cur)"ABC"Is this article helpful?
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