Javascript: How to sort an array of records by values in one of the fields?

Question

Possible Duplicate:
Sorting objects in an array by a field value in JavaScript

Suppose I have an array of records: [{a:0,b:0},{a:2,b:1},{a:1,b:2}] which I wish to sort in descending order of the a field in each record, and alert the sorted records as a new array (ie the new array would be [{a:2,b:1},{a:1,b:2},{a:0,b:0}]) - how would I go about this? I've tried a few approaches but am banging my head against the wall.

Thanks

Peter Bailey · Answer 1 · 2009-11-06T19:44:58.920

A straightforward approach

var sorted = [{a:0,b:0},{a:2,b:1},{a:1,b:2}].sort( function( a, b )
{
  if ( a.a == b.a ) return 0;
  return ( a.a > b.a ) ? 1 : -1;
}).reverse();

EDIT

And a more flexible approach

// Note: console.log() require Firebug

var records = [{a:0,b:0},{a:2,b:1},{a:1,b:2}];
console.log( records );

// Sorty by 'a' ascending
sortByProperty( records, 'a' );
console.log( records );

// Sort by 'b' descending
sortByProperty( records, 'b', true );
console.log( records );  

function sortByProperty( arr, property, descending )
{
  arr.sort( function( a, b )
  {
    return Boolean( descending )
      ? b[property] - a[property]
      : a[property] - b[property]
  } );
}

EDIT 2

A version that works for strings as well

// Note: console.log() require Firebug

var records = [
    {a:0,b:0}
  , {a:2,b:1}
  , {a:'banana',b:'apple'}
  , {a:1,b:2}
  , {a:'apple',b:'banana'}
];
console.log( records );

// Sorty by 'a' ascending
sortByProperty( records, 'a' );
console.log( records );

// Sort by 'b' descending
sortByProperty( records, 'b', true );
console.log( records );  

function sortByProperty( arr, property, descending )
{
  arr.sort( function( a, b )
  {
    var c = a[property].toString()
      , d = b[property].toString()

    if ( c == d ) return 0;
    return Boolean( descending )
      ? d > c ? 1 : -1
      : d < c ? 1 : -1 
  } );
}

Added an alternate solution that allows you to specify the property to sort by and an order with parameters. — Peter Bailey, Nov 06 '09 at 19:33

Corey Ballou · Answer 2 · 2009-11-06T19:30:20.187

0

Using closures is slower than directly referencing a function.

// assume var records = [{a:0,b:0},{a:2,b:1},{a:1,b:2}];
records.sort(myCustomSort);
function myCustomSort(a, b) {
    return (b.a - a.a);
}

If you really need a second variable for the new array, simply make a copy of the initial array prior to calling the custom sort method.

edited Nov 06 '09 at 19:30

answered Nov 06 '09 at 19:18

Corey Ballou

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score 0 · Answer 3 · answered Nov 06 '09 at 19:22

0

How about a sort delegate?

[{a:0,b:0},{a:2,b:1},{a:1,b:2}].sort(function(a,b){
    // see http://www.javascriptkit.com/javatutors/arraysort.shtml 
    // for an explanation of this next line
    return b.a-a.a;
});

(After saving, I noticed two other almost identical answers, but I'll leave mine here for the minor differences.)

answered Nov 06 '09 at 19:22

Brother Erryn

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Thanks for the reply (this applies to all three of you really!) The only problem is that it alerts "[object Object],[object Object],[object Object]" - is there any way I could convert the objects so that it alerts the array of sorted records correctly? Thanks again – Deacon Nov 06 '09 at 19:41
Why in the world did I get downvoted? For not immediately erasing my answer once I noticed it was a duplicate? To answer Deacon's question, well, I'd have to see exactly how you're trying to alert the results of the sort. – Brother Erryn Nov 06 '09 at 19:56
@Deacon - the best approach is to stop using alert() to debug and switch to something like Firebug instead. – Peter Bailey Nov 06 '09 at 20:38
@Peter Bailey, Firebug is awesome, as is `console.log()`, but the original questioner specifically asked for `alert()` ... maybe worth pointing out threads like http://stackoverflow.com/questions/103155/javascript-debugger to help people out. – artlung Nov 06 '09 at 21:01

score 0 · Answer 4 · answered Nov 06 '09 at 19:43

// your items array
var items = [{a:0,b:0},{a:2,b:1},{a:1,b:2}];
// function we can use as a sort callback
var compareItemsBy_a_Descending = function(x,y) {
  return y.a - x.a;
};
// function to alert the items array
var displayItems = function(items) {
  var out = [];
  for (var i=0;i<items.length;i++) {
    out.push('{a:' + items[i].a + ',b:' + items[i].b + '}');
  }
  alert('[' +out.join(',') + ']');
};

// run it
displayItems(items);

RESULT: [{a:0,b:0},{a:2,b:1},{a:1,b:2}]

// sort it
items.sort(compareItemsBy_a_Descending);

// run it again
displayItems(items);

RESULT: [{a:2,b:1},{a:1,b:2},{a:0,b:0}]

score 0 · Answer 5 · answered Nov 06 '09 at 20:30

Hughes my colleague just showed me today the following.
Note the use of -cmp() and cmp() for descending and ascending.

var cmp = function(x, y){ return x > y? 1 : x < y ? -1 : 0; },
    arr =  [{a:0,b:0},{a:2,b:1},{a:1,b:2},{a:2, b:2}];

// a ascending
arr.sort(function(x, y){
    return cmp(x.a, y.a) < cmp(y.a, x.a) ? -1:1;
});

// a descending
arr.sort(function(x, y){
    return -cmp(x.a, y.a) < -cmp(y.a, x.a) ? -1:1;
});

// a ascending, b descending
arr.sort(function(x, y){
    return [cmp(x.a, y.a), -cmp(x.b, y.b)] < [cmp(y.a, x.a), -cmp(y.b,x.b)] ? -1:1;
});

Javascript: How to sort an array of records by values in one of the fields?

5 Answers5

EDIT

EDIT 2