Custom javascript object sort and maintain index association

Question

The object

var obj = {
   uniquestring1:
   {
       obj1: 'content',
       obj2: 'content'
   },
   uniquestring2:
   {
       obj1: 'content'
   }
}

So i need to sort the object by number of the elements contained by the first parent element. The use of .sort function is not a sollution for me because i need to maintain the index assosiaction which array's dont keep.

The result should be:

var obj = {
   uniquestring2:
   {
       obj1: 'content'
   },
   uniquestring1:
   {
       obj1: 'content',
       obj2: 'content'
   }
}

You can't sort an object's properties because they are not an ordered array. Perhaps you want to iterate over the properties in a certain order? — js1568, Aug 30 '11 at 18:17
implement some sorting algorithm, don't use jquery .sort if it doesn't fit your case. http://stackoverflow.com/questions/220044/which-sort-algorithm-works-best-on-mostly-sorted-data — Marek Sebera, Aug 30 '11 at 18:18

jfriend00 · Accepted Answer · 2011-08-30T18:25:38.507

Javscript objects don't have a sort order so they can't be sorted. To sort, you must have an array somewhere and I see no array in your code.

Object keys have no defined order.

If you only need ordered access, use an array.
If you only need keyed access, use an object.
If you need access by both, you can use a parallel array, but this is a pain unless the data is not changing.

You could do a one-time creation of a parallel array that contained key references in sorted order like this:

var obj = {
   uniquestring1:
   {
       obj1: 'content',
       obj2: 'content'
   },
   uniquestring2:
   {
       obj1: 'content'
   }
}

var objOrder = [];   // sorted arrays that contains first level keys into obj
var num;
for (var i in obj) {
    objOrder.push(i);  // get all keys into the array
    num = 0;
    for (var j in obj[i]) {
        ++num;         // count items in each key object
    }
    obj[i].keyCnt = num;   // save this for later sorting purposes
}
// now sort the parallel array by keyCnt
objOrder.sort(function(a, b) {
    return(obj[a].keyCnt - obj[b].keyCnt);
});

Then, to traverse the keys in sorted order, you would do it like this:

for (var i = 0; i < sortedOrder.length; i++ ) {
    var item = obj[sortedOrder[i]];
    // do something with item here
}

Joe · Answer 2 · 2011-08-30T18:24:01.817

2

obj is a hash not an array, so you can't sort it. For example, obj[0]; // is undefined. Now if you had this:

var obj = {
   uniquestring1:
   {
       obj1: 'content',
       obj2: 'content'
   },
   uniquestring2:
   {
       obj1: 'content'
   }
};
var arr = [],

for(var i in obj) {
    arr.push(obj[i]);
}

arr.sort(function (a, b) {
   return Object.keys(a).length - Object.keys(b).length;
})

Then that sort would work, with Object.keys

edited Aug 30 '11 at 18:24

answered Aug 30 '11 at 18:17

Joe

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Of course i know that, that is why i've asked here for a workaround. – keepwalking Aug 30 '11 at 18:20
1

@keepwalking: why are you looking for a workaround? What's wrong with this? If you need your labels, you should wrap your objects in *yet another* object: {label: 'uniquestring1', value: { obj1: 'content', obj2: 'content' } – Joseph Silber Aug 30 '11 at 18:22
Keep in mind the the `.keys()` property of an object is not supported in older browsers such as IE6-IE8. – jfriend00 Aug 30 '11 at 18:28

Custom javascript object sort and maintain index association

2 Answers2