Sorting an Array of JavaScript Objects a Specific Order (using existing function)

Question

Given an array of objects:

{
    key: \"a\",
    value: 42
},
{
    key: \"d\",
    value: 28
},
{
    key: \"c\",
    value: 92
},
{
    key: \"b\",
    value: 8         


        

Answer 1

// create hash map el.key -> index, to help us with direct access, avoid searching
const hashMap = arr.reduce((acc, el, index) => { acc[el.id] = el; return acc }, {})

// finally, map the ids to the final result
const ids.map(id => hashMap[id])

Answer 2

Great answers provided so far. Thought that the following may also be an alternative solution in plain JS:

var arr = arr.sort(function(a,b) {
    return order.indexOf( a.key ) - order.indexOf( b.key );
    //for the sake of recent versions of Google Chrome use:
    //return a.key.charCodeAt(0) > b.key.charCodeAt(0); or return a.key.charCodeAt(0) - b.key.charCodeAt(0);
});

var arr = [
    {
        key: "a",
        value: 42
    },
    {
        key: "d",
        value: 28
    },
    {
        key: "c",
        value: 92
    },
    {
        key: "b",
        value: 87
    }
];

var order = ["c", "a", "b", "d"];

console.log( 'Original: ', JSON.stringify( arr ) );

var arr = arr.sort(function(a,b) {
      return order.indexOf( a.key ) - order.indexOf( b.key );
});

console.log( 'Ordered: ', JSON.stringify( arr ) );

Answer 3

I can't claim that this is the most efficient way, but you can use the key for each object as a key for properties in another object. Then simply access them by these keys.

for (x = 0; x < objn.length; x++) {
    newobj[objn[x].key] = objn[x];
}
objn = [];
for (x = 0; x < keys.length; x++) {
    objn.push(newobj[keys[x]]);
}
console.log(objn);

http://jsfiddle.net/WdehF/

Answer 4

Just use indexOf to convert the key to the correct order:

var order = ["c", "a", "b", "d"];
_.sortBy(arr, function(obj){ 
    return _.indexOf(order, obj.key);
});

Fiddle

If there are a lot of keys, then it would be advantageous to make a hash-map out of the array, like:

var order = ["c", "a", "b", "d"];
var orderMap = {};
_.each(order, function(i) { orderMap[i] = _.indexOf(order, i); });

This makes the key-sorting lookup constant time rather than O(n). (Fiddle)