Sorting only one property inside an array based on another property

Question

I have a Javascript array that has 2 properties id, sortedPosition.

I want to kind of fake sort the array based on id, and modify sortedPosition such that it reflects the sorted position of the object within that array.

For example:

Input array:

[
    {
        "id" : 34,
        "sortedPosition" : 2
    }, {
        "id" : 3,
        "sortedPosition" : 1
    }, {

        "id" : 344,
        "sortedPosition" : 0
    }
]

Output array:

[
    {
        "id" : 34,
        "sortedPosition" : 1
    }, {
        "id" : 3,
        "sortedPosition" : 0
    }, {
        "id" : 344,
        "sortedPosition" : 2
    }
]

I came upon a solution which looks pretty bad, it involves 2 extra copies of deepCloned arrays, and it doesn't seem right. There has to be a more elegant solution.

Thanks for any help.

Bergi · Accepted Answer · 2014-04-11 01:17:28Z

3

I came upon a solution which looks pretty bad, it involves 2 extra copies of deepCloned arrays

A shallow copy of the array should be enough:

arr.slice() // create new array with the same objects
 .sort(function(a,b){return a.id-b.id;}) // sort that (leave original untouched)
 .forEach(function(o,i){o.sortedPosition = i;}); // update the objects

answered Apr 11, 2014 at 1:17

Bergi

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1 Comment

bits Over a year ago

Thanks, your elegant solution is exactly the reason why I summoned SO's help.

Pointy · Accepted Answer · 2014-04-11 01:00:33Z

0

Sort the array and then update the position.

array.sort(function(a1, a2) {
  return a1.id - a2.id;
});

array.forEach(function(v, i) {
  v.sortedPosition = i;
});

edit if you just want to set the sorted position, you can do something like this:

var t = array.map(function(v) {
  return { v: v }
});
t.sort(function(v1, v2) { return v1.v.id - v2.v.id; });
t.forEach(function(v, i) { v.v.sortedPosition = i; });

That makes a new array with references to the objects in the original array, then sorts it, then fixes up the position properties. The ordering of the original array is unaffected. The pass to make a new array won't be very expensive; it's not really a "deep copy" at all.

edited Apr 11, 2014 at 1:00

answered Apr 11, 2014 at 0:44

Pointy

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2 Comments

bits Over a year ago

But this thing is that I don't want the array to be sorted. Just wish to update sortedPosition.

bits Over a year ago

I updated the order of objects in question to avoid this confusion.

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