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I have an array of objects of the following form:

arr[0] = { 'item1' : 1234, 'item2' : 'a string' };

I sort it first by 'item1' which is straightforward. Now i want to sort arr (which is sorted by 'item1') again but this time by 'item2' but only for the elements where 'item1' is the same. The final array would look like:

arr = [
  { 'item1' : 1234, 'item2' : 'apple' },
  { 'item1' : 1234, 'item2' : 'banana' },
  { 'item1' : 1234, 'item2' : 'custard' },
  { 'item1' : 2156, 'item2' : 'melon' },
  { 'item1' : 4345, 'item2' : 'asparagus' } 
];

I tried to write a sorting function for the second case like so:

arr.sort(function(a,b){
  if(a.item1 === b.item1){
    return a.item2 > b.item2 ? 1 : a.item2 < b.item2 : -1 : 0;
  }
});

I could combine the two sorts in one function to get the final sorted array but there will be cases where I'll have to sort by just 'item1' or just 'item2'.

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If you managed to sort by item1, item2, and both of them, then what are you asking exactly? –  Eran Zimmerman Aug 23 '11 at 7:32
 
So its like writing a decorator pattern where i say "new sortByItem2( new sortByItem1(arr))". I also want to use it like sortByItem1(arr) or sortByItem2(arr) or "new sortByItem1( new sortByItem2(arr))" –  fenderplayer Aug 23 '11 at 7:52

1 Answer

up vote 6 down vote

You can have four different comparison functions - one sorting by item1, one by item2, one by item1 then item2 and one by item2 then item1.

E.g.:

arr.sort(function(a,b){
  if(a.item1 == b.item1){
    return a.item2 > b.item2 ? 1 : a.item2 < b.item2 : -1 : 0;
  }

  return a.item1 > b.item1 ? 1 : -1;
});
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