Write a function “groupBy(array, callback)”

Question

I have a JavaScript task where I have to implement a function \"groupBy\", which, when given an array of objects and a function, returns an object w

Answer 1

It's a reduce() one-liner. Reduce allows you to loop through the array and append to a new object based on the logic of its callback. In this function a (for accumulated) is the object we're making and c (for current item) is each item in the loop taken one at a time.

It works especially concisely here because the function to make the object key is passed in:

var list = [{id: "102", name: "Alice"},
{id: "205", name: "Bob", title: "Dr."},
{id: "592", name: "Clyde", age: 32}];

function groupBy(list, Fn) {
    return list.reduce((a, c) => (a[Fn(c)] ? a[Fn(c)].push(c) : a[Fn(c)] = [c], a), {})
}

var t = groupBy(list, function(i) { return i.id; });
console.log(t)

var l = groupBy(list, function(i) { return i.name.length; });
console.log(l)