Sort an array of objects based on another array of ids

Question

I have 2 arrays

a = [2,3,1,4]
b = [{id: 1}, {id: 2}, {id: 3}, {id: 4}]

How do I get b sorted based on a? My desir

Answer 1

Here's an alternative construction using Ramda that might be a bit more succinct, and the functions are pretty easy to repurpose for other things.

const {indexBy, prop, map, flip} = R
const a = [2,3,1,4]
const b = [{id: 1}, {id: 2}, {id: 3}, {id: 4}]

const toIndexById = indexBy(prop('id'))
const findIndexIn = flip(prop)

const c = map(findIndexIn(toIndexById(b)), a)
console.log(c)

<script src="https://cdnjs.cloudflare.com/ajax/libs/ramda/0.27.1/ramda.min.js"></script>

Answer 2

This solution uses Array#sort with a helper object c for the indices.

{
    "1": 2,
    "2": 0,
    "3": 1,
    "4": 3
}

var a = [2, 3, 1, 4],
    b = [{ id: 1 }, { id: 2 }, { id: 3 }, { id: 4 }],
    c = a.reduce(function (r, a, i) {
        r[a] = i;
        return r;
    }, {});

b.sort(function (x, y) {
    return c[x.id] - c[y.id];
});

document.write('<pre>' + JSON.stringify(b, 0, 4) + '</pre>');

For greater objects, I suggest to use Sorting with map.

Answer 3

Plain javascript, using some methods of the Array (ES2015 standard)

var a = [2,3,1,4];
var b = [{id: 1}, {id: 2}, {id: 3}, {id: 4}];
var c = [];

a.forEach(el => c.push(b.find(e => e.id == el)));

document.write(JSON.stringify(c, 0, 2));

Answer 4

Or may be simpler

b.sort(function(obj1,obj2){
   return a.indexOf(obj1.id) > a.indexOf(obj2.id)
});