Question

I have:

function getRandomInt(min, max){
        return Math.floor(Math.random() * (max - min + 1)) + min;
}

But the problem is I want randomise the population of something with elements in an array (so they do not appear in the same order every time in the thing I am populating) so I need to ensure the number returned is unique compared to the other numbers so far.

So instead of:

   for(var i = 0; i < myArray.length; i++) {

   }

I have:

var i;
var count = 0;
while(count < myArray.length){
  count++;
  i = getRandomInt(0, myArray.length); // TODO ensure value is unique

  // do stuff with myArray[i];
}

Answer 1

It looks like rather than independent uniform random numbers you rather want a random permutation of the set {1, 2, 3, …, N}. I think there’s a shuffle method for arrays that will do that for you.

---

As requested, here’s the code example:

function shuffle(array) {
  var top = array.length;
  while (top--) {
      var current = Math.floor(Math.random() * top);
      var tmp = array[current];
      array[current] = array[top - 1];
      array[top - 1] = tmp;
    }
  return array;
}