Is it correct to use JavaScript Array.sort() method for shuffling?

Question

I was helping somebody out with his JavaScript code and my eyes were caught by a section that looked like that:

function randOrd(){
  return (Math.round(Math         


        

Answer 1

Interestingly, Microsoft used the same technique in their pick-random-browser-page.

They used a slightly different comparison function:

function RandomSort(a,b) {
    return (0.5 - Math.random());
}

Looks almost the same to me, but it turned out to be not so random...

So I made some testruns again with the same methodology used in the linked article, and indeed - turned out that the random-sorting-method produced flawed results. New test code here:

function shuffle(arr) {
  arr.sort(function(a,b) {
    return (0.5 - Math.random());
  });
}

function shuffle2(arr) {
  arr.sort(function(a,b) {
    return (Math.round(Math.random())-0.5);
  });
}

function shuffle3(array) {
  var tmp, current, top = array.length;

  if(top) while(--top) {
    current = Math.floor(Math.random() * (top + 1));
    tmp = array[current];
    array[current] = array[top];
    array[top] = tmp;
  }

  return array;
}

var counts = [
  [0,0,0,0,0],
  [0,0,0,0,0],
  [0,0,0,0,0],
  [0,0,0,0,0],
  [0,0,0,0,0]
];

var arr;
for (var i=0; i<100000; i++) {
  arr = [0,1,2,3,4];
  shuffle3(arr);
  arr.forEach(function(x, i){ counts[x][i]++;});
}

alert(counts.map(function(a){return a.join(", ");}).join("\n"));