/* libRandomTools.js */
/* Mike Wilson, April 4, 2005 */
/* Anyone may copy and/or modify this software without restriction. */

/*
IMPORT: ()
EXPORT: randomChoose, randomize
*/

function randomChoose (a) {
    /* Given an array A, choose and return one element. */
    var result;
    var len = a.length;
    result = undefined;
    if (len != 0) {
        var i = Math.floor(Math.random() * len);
        result = a[i];
    }
    return result;
}

function randomize (a) {
    /* Given an array A, take all the elements, mix them up,
       and return them in a new array D.
    */
    var len = a.length;
    var b = new Array(len);
    var c = new Array(len);
    var d = new Array(len);
    /* b = array of indices: 0,1,2,... */
    var i, j=0;
    for (i=0 ; i<len ; i++)
        b[i] = j++;
    /* c = indices mixed up, 8,1,4,... */
    for (i=0 ; i<len ; i++) {
        j = Math.floor(Math.random() * b.length);
	c[i] = b[j];
	b.splice(j,1);
    }
    /* d = array with original elements, mixed up */
    for (i=0 ; i<len ; i++)
	d[i] = a[c[i]];
    delete b;
    delete c;
    return (d);
}

function testRandom () {
    var basket = ["a", "b", "c", "d", "e", "f"];
    var counts = new Array(basket.length);
    var i,j;
    for (i=0 ; i<basket.length ; i++)
        counts[i] = 0;
    for (i=0 ; i<600 ; i++) {
        var one = randomChoose(basket);
        for (j=0 ; j<basket.length ; j++)
            if (basket[j] == one)
	        counts[j]++;
    }
    alert(counts.join(" "));
    return;
}