Shuffler

shuffler.js

// Randomly samples an element from an array and prevents the same element 
// from being returned twice unless separated by some number of samples
//
// Constructor parameters
// array: the original array to shuffle and use
// proximityLimit: minimum number of samples between returning the same element (max: array.length/2)
// Methods
// Next(): get the next item
//
// sample use:
// var myShuffler = new Shuffler([1,2,3,4,5,6,7,8,9,0], 3);
// var x = myShuffler.Next();
function Shuffler(array, proximityLimit) {
    var original = array;
    var similarRange = Math.min(proximityLimit, array.length/2);
    var previous = [];
    var current = [];
    var currentIndex = 0;

    // Fisher-Yates shuffle
    function shuffle(array) {
        var m = array.length, temp, i;
        // While there remain elements to shuffle…
        while (m) {
            // Pick a remaining element…
            i = Math.floor(Math.random() * m--);
            // And swap it with the current element.
            temp = array[m];
            array[m] = array[i];
            array[i] = temp;
        }
        return array;
    }

    // test if two arrays have any similar items
    function testSimilar(array1, array2) {
        for (var i = 0; i < array1.length; i++) {
            if (array2.indexOf(array1[i]) >= 0)
                return true;
        }
        return false;
    }

    // get the next set of shuffled items
    function makeNewSet() {
        previous = current;
        var tailPrevious = previous.slice(previous.length - similarRange);
        var headCurrent = [];
        do {
            current = shuffle(original);
            headCurrent = current.slice(0, proximityLimit);
        } while (testSimilar(tailPrevious, headCurrent))
    }

    // returns a random element
    this.Next = function () {
        if (currentIndex >= current.length) {
            currentIndex = 0;
            makeNewSet();
        }
        return current[currentIndex++];
    }
}