How to group an array of objects by a key in JavaScript

In this Article we will go through how to group an array of objects by a key only using single line of code in JavaScript. This is a one-line JavaScript code snippet that uses one of the most popular ES6 features => Arrow Function.

Let's define this short function:

const groupBy = (arr, key) => arr.reduce((acc, item) => ((acc[item[key]] = [...(acc[item[key]] || []), item]), acc), {});

#Example

groupBy([
    { branch: 'audi', model: 'q8', year: '2019' },
    { branch: 'audi', model: 'rs7', year: '2020' },
    { branch: 'ford', model: 'mustang', year: '2019' },
    { branch: 'ford', model: 'explorer', year: '2020' },
    { branch: 'bmw', model: 'x7', year: '2020' },
], 'branch');

/*
{
    audi: [
        { branch: 'audi', model: 'q8', year: '2019' },
        { branch: 'audi', model: 'rs7', year: '2020' }
    ],
    bmw: [
        { branch: 'bmw', model: 'x7', year: '2020' }
    ],
    ford: [
        { branch: 'ford', model: 'mustang', year: '2019' },
        { branch: 'ford', model: 'explorer', year: '2020' }
    ],
}
*/
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