Unusual results when sorting an array of objects by a property each object has

Question

I'm trying to sort an array of objects by a property rank which each object has. This seems to be the accepted way of doing it. However, it does not seem to be working correctly.

var waypoints = ig.game.getEntitiesByType(EntityWaypoint); // returns array of objects
// This line tells sort to order by Array[i].rank
waypoints.sort(function(a,b) {return (a.rank < b.rank) ? -1 : (a.rank > b.rank) ? 1 : 0;});
waypoints.sort();
for( var i=0; i<waypoints.length; i++ ) {
    console.log(waypoints[i].rank);
}

Console ends up looking like this:

I've also tried the following variation which results in the same thing.

waypoints.sort(function(a,b) {return (parseInt(a.rank) < parseInt(b.rank)) ? -1 : (parseInt(a.rank) > parseInt(b.rank)) ? 1 : 0;});

Why isn't this properly sorting an array of objects by the rank property of each object?

You should be able to do just return a.rank - b.rank;, the subtraction will force rank to be converted to a number (if it can be). — RobG
– RobG, Commented Feb 28, 2013 at 5:02
waypoints.sort(function(a,b) {return a.rank - b.rank;}); seems to work, but I have no idea why. Does this method only work for numbers or would it work for words? — Joncom
– Joncom, Commented Feb 28, 2013 at 5:58
For some version of "work", yes, but probably not how you expect. The comment above has a link to the internal ToNumber algorithm, and the special treatment of strings. Essentially if the string converts to a number literal (e.g. "12" -> 12), then that happens. Other strings (e.g. "foo" -> NaN) not so. — RobG
– RobG, Commented Feb 28, 2013 at 9:35

Matt Ball · Accepted Answer · 2013-02-28 05:02:43Z

3

There is nothing wrong with your custom sort. Your first piece of code calls waypoints.sort() twice. The second sort is mucking with the ordering; remove it.

answered Feb 28, 2013 at 5:02

Matt Ball

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2 Comments

Joncom Over a year ago

Worked great, thank you! Seems strange though that sorting a sorted array could unsort it...

RobG Over a year ago

Because the first sort is sorting numbers, the second is sorting objects. The algorithm is in ECMA-262.

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