Underscore.js _.reductions() Method

The _.reductions() method is used to transform an array of elements to an array in which every intermediate value in the folding operation is stored. This method is the same as _.reduce() method except it returns an array.

An array, a function, and a starting value are passed in this method to generate a new array to perform operations on the array.

Syntax:

_.reductions(array, function, start_val)

Parameters:

• array: The array to be work upon.
• function: The function containing iteration conditions.
• start_val: The value passed at starting which further updates on further operations.

Return Value: This method returns a new array.

Note: This will not work in normal JavaScript because it requires the underscore.js contrib library to be installed.  Underscore.js contrib library can be installed using npm install underscore-contrib --save.

Example 1: In this example, we will generate an array using this method. Here, the sum array is generated with starting value given as 0 which updates on addition operations.

Javascript

// Defining underscore contrib variable
var _ = require('underscore-contrib');

// Defining Array
var array = [10, 12, 23, 34, 45];

var arr =_.reductions(array, function(st, n) {
  return st + n;
}, 0);
console.log("Generated Array : ");
console.log(arr);

Output:

Generated Array :
[ 10, 22, 45, 79, 124 ]

Example 2: In this example, we will generate a multiplication array by giving starting value as 1 which updates on further multiplication.

Javascript

// Defining underscore contrib variable
var _ = require('underscore-contrib');

// Defining Array
var array = [10, 12, 23, 34, 45];

var arr =_.reductions(array, function(st, n) {
  return st * n;
}, 1);
console.log("Generated Array : ");
console.log(arr);

Output:

Generated Array :
[ 10, 120, 2760, 93840, 4222800 ]