How to randomize subset of array in Javascript?

Question

What is the best way to randomize part of the array in Javascript

For example, if I have 100 items in the array, what is the fast and efficient way of randomizing set of

Answer 1

The following shuffles the specified chunk of an array in place, as randomly as the environment's random number generator will allow:

function shuffleSubarray(arr, start, length) {
    var i = length, temp, index;
    while (i--) {
        index = start + Math.floor(i * Math.random());
        temp = arr[index];
        arr[index] = arr[start + i];
        arr[start + i] = temp;
    }
    return arr;
}

var a = [1, 2, 3, 4, 5, 6, 7, 8, 9];
alert( shuffleSubarray(a, 2, 5) );

Answer 2

You can adjust the array shuffle method that is described here: http://jsfromhell.com/array/shuffle

It is based on Fisher-Yates (Knuth) algorithm (http://en.wikipedia.org/wiki/Fisher–Yates_shuffle).

Answer 3

I would split the 1 array into 10 subsets, then perform a shuffle algorithm of your choice on those subsets, and then recombine in the correct order.

Answer 4

I would just use the built in slice, concat and sort methods. Something like this.

function shuffle(arr, start, end) {
 return arr.slice(start, end).sort(function() { return .5 - Math.random(); }).concat(arr.slice(end));
};

That's the basic idea, you probably want to make an algorithm to slice every 10 elements, sort and rejoin the sets.

EDIT: Read comments below for why this solution may not be suitable for your needs.