distributedRandomSample.js

// this file is not scope. You must use it inside a anonymus function and save in windows RandomList and RandomList2 or export those

function createWeightedList (list, weight) {
  var weighed_list = [];
  for (var i = 0; i < weight.length; i++) {
    var multiples = weight[i] * 100;
    for (var j = 0; j < multiples; j++) {
      weighed_list.push(list[i]);
    }
  }

  return weighed_list;
}

function RandomList (list, weight) {
  this.weighed_list = createWeightedList(list, weight);
  this.length = this.weighed_list.length;
}

RandomList.prototype.next = function () {
   return this.weighed_list[Math.floor(Math.random() * this.length)];
}

function RandomList2 (list, weight) {
  this.list = list;
  this.weight = weight;
  this.total_weight = this.weight.reduce(function (prev, cur, i, arr) {
    return prev + cur;
  });
}

RandomList2.prototype.rand = function rand (min, max) {
    return Math.random() * (max - min) + min;
};

RandomList2.prototype.next = function next () {
    var random_num = this.rand(0, this.total_weight);
    var weight_sum = 0;
    for (var i = 0; i < this.list.length; i++) {
        weight_sum += this.weight[i];
        weight_sum = +weight_sum.toFixed(2);
         
        if (random_num <= weight_sum) {
            return this.list[i];
        }
    }
};

test.js

var list = new RandomList(['a', 'b', 'c'], [0.33, 0.33, 0.33]);
var listAnother = new RandomList2(['a', 'b', 'c'], [0.33, 0.33, 0.33]);

function fullCount (listOne, listTwo, until) {
  return [count(listOne, until), count(listTwo, until)];
}

function count (list, until) {
  var i = 0;
  var count = { a: 0, b: 0, c: 0 };
  while (i <= until) {
    var value = list.next();
    if (value === 'a') { count.a += 1; }
    else if (value === 'b') { count.b += 1; }
    else if (value === 'c') { count.c += 1; }
    i++;
  }
  return count;
}

console.log(fullCount(list, listAnother, 100));
console.log(fullCount(list, listAnother, 100));
console.log(fullCount(list, listAnother, 100));
console.log(fullCount(list, listAnother, 100));
console.log(fullCount(list, listAnother, 100));