Sorting an array of objects according to one of their properties

Question

I don't know if this is a peculiar case, but the problem is quite simple at hand. Let's say you have an array which defines the order in which your objects must be sorted. Let's say this array is like this one:

var sort = [5, 1, 6];

This array order is arbitrary (the numbers aren't sorted according to any specific rule), and the sorted array of objects must follow the order in which the items in the sort array appear)

And you have an array of objects, like this one:

var obj = [{id: 1}, {id: 6}, {id:5}];

So the result (according to the order in sort and the value of each object's id), should be this:

obj = [{id: 5}, {id: 1}, {id:6}];

I have tried this approach:

var obj = [{id: 1}, {id: 6}, {id:5}];
var sort = [5, 1, 6];

var indexedObjArr = [],
    tmpObj = {};
obj.forEach(function(item) {
    tmpObj[item.id] = item;
    indexedObjArr.push(tmpObj);
    tmpObj = {};
});
obj = [];

//This is where it fails, obj ends up having all undefined entries
indexedObjArr.forEach(function(item, i) {
    // [sort[i]] === undefined, but sort[i] gives an actual number (e.g. 5),
    // and, for instance item[5], gives back the correct item
    obj.push(item[sort[i]]);
});
console.log(obj);

What am I doing wrong in this script? Or can you think of a better approach to the problem?

Thank you.

Answer 1

Why not just use the built in sort method for Arrays?

obj.sort(function(a, b) { return sort.indexOf(a.id) - sort.indexOf(b.id) });

var obj = [{id: 1}, {id: 6}, {id: 5}];
var sort = [5, 1, 6];

console.log(obj.sort(function(a, b) {
  return sort.indexOf(a.id) - sort.indexOf(b.id)
}));

Answer 2

Flaw in your code: indexedObjArr will look like [ { 1: id1item}, {6: id6item}, {5: id5item} ]

Clearly when you iterate over this array, item object will be one of the items in the array e.g. { 1 : id1item }. Now if you try to do item[sort[i]] i.e. item[5] this will be undefined obviously.

Try this (only corrections... update your code):

var indexedObj = {};//object not array
obj.forEach(function(item) {
    indexedObj[item.id] = item;
});
//now the indexedObj will be { 1 : id1item, 6: id6item,...}

obj = [];

//run the loop in the order you want the sorting i.e. [5, 1, 6]
sort.forEach(function(id) {
    obj.push(indexedObj[id]);//get the item for id as in the sort array
});

console.log(obj);

Another issue with this approach is sort array is assumed to be of the same size as the array. If that's not the case, then special handling will be required. One solution for that could be:

sort.forEach(function(id) {
    obj.push(indexedObj[id]);
    //remove the processed id from indexedObj
    delete indexedObj[id];
});
//now add all the objects left out.
for(var item in indexedObj) {
    obj.push(indexedObj[item]);
}

Answer 3

One might use a middle-man to fetch the appropriate item from the root source, such as with "findObj" here. There's probably a more elegant way to do this, but a "brute force" approach like this will get you there.

var obj = [{id: 1}, {id: 6}, {id:5}];
var sort = [5, 1, 6];
var result = [];
var findObj = function(id){
    for (var i = 0; i < obj.length; i++){
        if (obj[i].id === id){return obj[i];}
    };
    return null;
};
for (var pos = 0; pos < sort.length; pos++){
    result.push(findObj(sort[pos]));
}
console.log(JSON.stringify(result));

I created a solution here: http://jsfiddle.net/pp3qzowz/ Hope this helps.

Answer 4

Here is my solution :) I hope it help !

    var obj = [{id: 1}, {id: 6}, {id:5}];
var sort = [5, 1, 6];

var indexedObjArr = [],
    sortedObj = [];
sort.forEach(function(item) {
    obj.forEach(function(objItem){
        if(objItem.id == item)
            sortedObj.push(objItem);
    });
});
console.log(sortedObj);