// Made as proof of concept - malulleybovo@2019

// A simple and fair array shuffle algorithm
var randomizeArray = function(arr) {
    if (arr == null || !Array.isArray(arr)) return [];
    arr = arr.slice(0);
    var randArr = [];
    while (arr.length > 1) {
        randArr.push(arr.splice(
            Math.floor(Math.random() * arr.length), 1));
    }
    if (arr.length == 1) randArr.push(arr[0]);
    return randArr;
}

var N = 10; // Array size
var M = 100000; // Number of tests
var deviations = []; // Standard deviation per array position

// Create the test array
var arr = [];
for (var i = 0; i < N; i++) arr.push(i);
// Test fairness of algorithm
for (var i = 0; i < N; i++) {
    var prob = [];
    for (var j = 0; j < arr.length; j++) prob.push(0);
    // Get the distribution per element of the original array
    for (var j = 0; j < M; j++) {
        var testArr = randomizeArray(arr);
        prob[arr.indexOf(parseInt(testArr[i], 10))] += 1 / M;
    }
    // Get standard deviation for every position of the random array
    var avg = 0;
    for (var j = 0; j < N; j++) {
        avg += Math.pow(prob[j] - (1 / N), 2);
    }
    avg /= N;
    avg = Math.sqrt(avg);
    // Save results
    deviations.push(avg);
}

console.log("Standard Deviation per Array Position: " + deviations);