Lodash _.groupBy() Method

Lodash _.groupBy() method creates an object composed of keys generated from the results of running each element of collection through the iterate function. The order of the grouped values is determined by the order they occur in the collection. Also, the corresponding value of each key is an array of elements responsible for generating the key.

Syntax:

_.groupBy(collection, [iteratee]);

Parameters:

• collection: It is the collection that the method iterates over.
• iteratee: It is the function that is invoked for every element in the array.

Return Value:

This method returns the composed aggregate object.

Example 1: In this example, we are composing an array-by-length function where the array is grouped by the length of the strings.

javascript

// Requiring the lodash library
const _ = require("lodash");

// Original array
let users = (['eight', 'nine', 'four', 'seven']);

// Using of _.groupBy() method
// with the `_.property` iteratee shorthand
let grouped_data = _.groupBy(users, 'length')

console.log(grouped_data);

Output:

{ '4': [ 'nine', 'four' ], '5': [ 'eight', 'seven' ]}

Example 2: In this example, we are composing an array by in which array is grouped according to the Math.floor function.

javascript

// Requiring the lodash library
const _ = require("lodash");

// Original array
let users = (['one', 'two', 'three', 'four']);
let obj = ([3.1, 1.2, 3.3]);

// Using the _.groupBy() method
// with the `_.property` iteratee shorthand
let grouped_data = _.groupBy(users, 'length')
let grouped_data2 = _.groupBy(obj, Math.floor)

// Printing the output
console.log(grouped_data, grouped_data2);

Output:

{ '3': [ 'one', 'two' ], '4': [ 'four' ], '5': [ 'three' ] } 
{ '1': [ 1.2 ], '3': [ 3.1, 3.3 ] }