knuth-shuffle

The Fisher-Yates (aka Knuth) shuffle for Browser and Node.js

The Fisher-Yates (Knuth) Shuffle

As Microsoft learned the hard way (see article below), function random() { return 0.5 - Math.random() } turns out to be no-so-random at all.

The fisher-yates shuffle is an algorithm so simple that not even IEEE floating point math can screw it up!

I put this on npm as knuth-shuffle because fisher-yates-shuffle was just too long of a name and shuffle was already taken.

Browser Example

<script src="https://raw.github.com/coolaj86/knuth-shuffle/master/index.js"></script>

(function () {
  'use strict';

  var a = [2,11,37,42]
    , b
    ;

  // The shuffle modifies the original array
  // calling a.slice(0) creates a copy, which is assigned to b
  b = window.knuthShuffle(a.slice(0));
  console.log(b);
}());

Node Example

npm install -S knuth-shuffle

(function () {
  'use strict';

  var shuffle = require('knuth-shuffle').knuthShuffle
    , a = [2,11,37,42]
    , b
    ;

  // The shuffle modifies the original array
  // calling a.slice(0) creates a copy, which is assigned to b
  b = shuffle(a.slice(0));
  console.log(b);
}());

See Also

• Mike Bostock's Fisher–Yates Shuffle Visualization
• How to randomize/shuffle a JavaScript array
• Fisher-Yates Shuffle on Wikipedia
• Doing the Microsoft Shuffle: Algorithm Fail in Browser Ballot
• knuth-shuffle on NPM