JavaScript group an array of objects by key

In this article, I will explain about the groupBy array of object in javascript.

I will explain this using one example.

const cars = [{
make: "audi",
model: "r8",
year: "2012"
},
{
make: "audi",
model: "rs5",
year: "2013"
},
{
make: "ford",
model: "mustang",
year: "2012"
},
{
make: "ford",
model: "fusion",
year: "2015"
},
{
make: "kia",
model: "optima",
year: "2012"
}];

Now I am going group using make. For example ‘make:’audi’’ to ‘audi: {[…..]}’. We use to reduce function.

Reduce

The reduce() method executes a reducer function (that you provide) on each member of the array resulting in a single output value.

let group = cars.reduce((r, a) => {
 console.log("a", a);
 console.log('r', r);
 r[a.make] = [...r[a.make] || [], a];
 return r;
}, {});
console.log("group", group);

The output should be like this.

JavaScript groupBy

Another way:

Using lodash we can write simply.

lodash.groupBy(cars, 'make')

We can get the same output.

Thank you for reading.

Array.prototype.reduce()

Lodash