Sort array into custom order

Question

I have an array of objects that I want sorted in an unconventional way.

[
  {
    type: 'web',
    id: 1
  },
  {
    type: 'graphics',
    id: 2
  },
  {
    type: 'UX',
    id: 3
  },
  {
    type: 'custom',
    id: 4
  }
]

How would I go about sorting this array by object.id so they appear in the order 1, 3, 4, 2 instead?

@falinsky: that answers a different question, but this question has definitely been asked before. Let me look. — Scott Sauyet, Nov 19 '20 at 14:28
@ScottSauyet I apologize if that's the case, I was trying to look through similar questions but couldn't find the correct search term for it i guess. — Oliver Birch, Nov 19 '20 at 16:46
@Oliver: It's not a big deal. We close as duplicates so that there can be definitive answers to common questions, but it took me a bit of searching to find a correct duplicate, too. Please let us know if neither one is a reasonable answer to your question. — Scott Sauyet, Nov 19 '20 at 17:14

Mihai Alexandru-Ionut · Answer 1 · 2020-11-19T13:45:51.247

1

You could use an order array for achieving this.

Creating a dictionary is more efficient than using indexOf method because the lookup for the dictionary is O(1).

var array = [ { type: 'web', id: 1 }, { type: 'graphics', id: 2 }, { type: 'UX', id: 3 }, { type: 'custom', id: 4 } ];

var order = [1, 3, 4, 2];
var orderDict =  order.reduce((acc, item, index) => {
  acc[item] = index;
  return acc;
}, {});

array.sort((a, b) => orderDict[a.id] - orderDict[b.id]);
console.log(array);

edited Nov 19 '20 at 13:45

answered Nov 19 '20 at 13:36

Mihai Alexandru-Ionut

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Yes, a dictionary will be more efficient... eventually. But the size of the data is important too. I'd be surprised if the costs of creating the dictionary are outweighed by the `O(n)` lookup in an array for a few entries or even a few dozen. Be wary of premature optimizations. – Scott Sauyet Nov 19 '20 at 14:16
@ScottSauyet, yes, creating dictionary is `O(n)` but `indexOf` has complexity `O(n)` because is unsorted array and it's executed many times while `sort` is executing. – Mihai Alexandru-Ionut Nov 19 '20 at 14:23
But do you think that for the example of four items this would be more faster than the simpler `indexOf` answer? – Scott Sauyet Nov 19 '20 at 14:27
For this small case, `indexOf` is faster. (https://jsbench.me/o4khoxzxiz/1) I don't know where the break-even point would be. – Scott Sauyet Nov 19 '20 at 14:42
@ScottSauyet, yes, you're right. For small case, `indexOf` is faster, but for large numbers https://jsbench.me/39khoygebu/1 the performance difference is huge and my approach wins. – Mihai Alexandru-Ionut Nov 19 '20 at 14:55
1

Yes, that's all I was saying. You can see in one of the duplicates that I was suggesting your approach, but if this case is as small as suggested, I would suggest the simpler code. – Scott Sauyet Nov 19 '20 at 15:10

score 0 · Accepted Answer · answered Nov 19 '20 at 13:44

sort in javascript can use original function.

arr=[
    {
      type: 'web',
      id: 1
    },
    {
      type: 'graphics',
      id: 2
    },
    {
      type: 'UX',
      id: 3
    },
    {
      type: 'custom',
      id: 4
    }
  ]

sort_key=[1,3,2,4]

arr.sort((a,b)=>sort_key.indexOf(a.id)-sort_key.indexOf(b.id))

Sort array into custom order

2 Answers2