flash on 2011-2-11

Array shuffle oneliner.

by makc3d 11 Feb 2011

Related works: 1

Talk

wh0 at 12 Feb 2011 08:58

Here's an article about Microsoft's use of this kind of shuffling. http://www.robweir.com/blog/2010/02/microsoft-random-browser-ballot.html

9re at 12 Feb 2011 15:49

the above link mentions the defeats of this algorithm. i can give you a simple example. from the sequence 1, 2, 3 with an arbitrary natural number n (i include zero) [1, 2, 3] requires 2n times swapping of it's elements [2, 1, 3], [1, 3, 2], [3, 2, 1] requires 2n + 1 times swapping [2, 3, 1], [3, 1, 2] requires 2(n + 1) times swapping (you may know this as 'odd permutation' or 'even permutation') and not only 'parity' of the permutation but also the algorithm inside Array.sort does have effects on the distribution i did a distribution test on Fisher-Yates algorithm and Array.sort with random comparing function. http://wonderfl.net/c/5NW

makc3d at 12 Feb 2011 16:36

sure, non-randomness due to sort() implementation is (or should be:) expected. @9re, /c/5NW is not a valid url (needs one more character)

makc3d at 12 Feb 2011 16:40

oh, it's http://wonderfl.net/c/5NWR

9re at 12 Feb 2011 17:02

sorry. that's it. http://wonderfl.net/c/5NWR

Embed

package  {
	import com.actionscriptbible.Example;
	/**
	 * Array shuffle oneliner.
	 */
	public class ShuffleArray extends Example {
		public function ShuffleArray () {
			var a:Array = [];
			for (var i:int = 0; i < 100; i++) a [i] = i;
			a.sort (function (a:*, b:*):Number { return (Math.random () > 0.5) ? 1 : -1; });
			trace (a);
		}
	}
}