Array Sorting in an object in javascript

Question

I have to sort the arrays of the "Key" in ascending order and here's what I am doing .

Surprsingly the first array is getting sorted in descending order and the next two in ascending order . Whats the possible reason for this?

var MainObject4 = [{ "mainarray": [{ "Key": [9,768,78] },
{ "Key": [9,4,1] },{ "Key": [49,89,54] }]
}];

var first = MainObject4[0];
 Object.keys(MainObject4[0]).forEach(function (k) {
   first[k].forEach(function (j) { 
        Object.keys(j).forEach(function (g) {
                    j[g].sort();   
      },this);
  },this);
 },this);

 alert(JSON.stringify(MainObject4, 0, 4));

Expected output:

[9,78,768]
[1,4,9]
[49,54,89]

Output I am getting now:

[768,78,9]
[1,4,9]
[49,54,89]

[768,78,9] is sorted, lexicographically. Try passing a comparison function, e.g function(x, y) { return x-y; } — orip
– orip, Commented Jan 25, 2017 at 11:05

A.Perrot · Accepted Answer · 2017-01-25 11:04:22Z

2

See the doc of Array.sort()

The default sort order is according to string Unicode code points.

If you want to compare numbers, you need to provide the comparison function, as said in the doc :

To compare numbers instead of strings, the compare function can simply subtract b from a.

answered Jan 25, 2017 at 11:04

A.Perrot

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Comments

Magicprog.fr · Accepted Answer · 2017-01-25 11:06:53Z

1

You need to add a function to compare sort parameters:

var MainObject4 = [{
    "mainarray": [{
        "Key": [9, 768, 78]
    }, {
        "Key": [9, 4, 1]
    }, {
        "Key": [49, 89, 54]
    }]
}];

var first = MainObject4[0];

Object.keys(MainObject4[0]).forEach(function(k) {
    first[k].forEach(function(j) {
        Object.keys(j).forEach(function(g) {
            j[g].sort(function(a, b) {
            	return a - b;
            });
        }, this);
    }, this);
}, this);

alert(JSON.stringify(MainObject4, 0, 4));

answered Jan 25, 2017 at 11:06

Magicprog.fr

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Comments

IVN · Accepted Answer · 2017-01-25 11:17:47Z

1

var MainObject4 = [{ "mainarray": [
    { "Key": [9,768,78] },
    { "Key": [9,4,1] },
    { "Key": [49,89,54] }
  ]
}];


MainObject4[0].mainarray.forEach(function (j) { 
    Object.keys(j).forEach(function (g) {
                j[g].sort(function (a, b) {
            return a - b;
        });   
    },this);
},this);

alert(JSON.stringify(MainObject4, 0, 4));

answered Jan 25, 2017 at 11:17

IVN

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Comments

Sathibabu · Accepted Answer · 2017-01-25 11:48:04Z

0

It's happening because of JavaScript's sort method takes by default unicode to compare the elements. For sorting numbers, you have to explicitly write a call back function to compare elements. For ex

var input = [1,20,2,12];
console.log(input.sort());// prints 1,12,2,20 
console.log(input.sort(function(a,b){
   return a-b;
}));// prints 1,2,12,20

So, You just need to add the compare function to your sort. That's all

answered Jan 25, 2017 at 11:48

Sathibabu

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