Lodash _.reductions() Method

Lodash is a JavaScript library that works on the top of underscore.js. Lodash helps in working with arrays, strings, objects, numbers, etc.

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 the _.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: This method accepts three parameters as mentioned above and described below:

• array: It is the array to be worked upon.
• function: It is the function containing the iteration conditions.
• start_val: It is 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 Lodash contrib library to be installed. Lodash contrib library can be installed using npm install lodash-contrib –save

Example 1: In this example, the sum array is generated with the starting value given as 0 which updates on addition operations.

Javascript

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

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

// Using the _.reductions() method
var arr = _.reductions(array, function(st, n) {
    return st - n;
}, 0);

console.log("Generated Array : ");
console.log(arr);

Output:

[ -10, -22, -45, -79, -124 ]

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

Javascript

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

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

// Using the _.reductions() method
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 ]