Run JavaScript function 70% of the time, randomly selected from an array of functions

Question

I've seen How to run a randomly selected function in JavaScript? which allows for running a JavaScript function randomly selected from at array with an equal chance each time (e.g. if there are two functions in total, there is a 50% chance that each function will be executed each time).

How to write a function to state the percentage chance of executing each function that is randomly available to be chosen from an array of functions? How do I do a weighted randomization??

function randomFrom(array) {
    return array[Math.floor(Math.random() * array.length)];
}
var contentWrapper = function (target,type,articleId) {
  // list type ads
  if (type == 'list') {
    function randomListData() {
      var func = randomFrom([
        function () {
          fnNameA10(target, 'list');
        },
        function () {
          fnNameB20(target, 'list', articleId);
        }
      ]);
      (func)();
    }
    randomListData();
    // content type ads
  } else if (type == 'content') {
    function randomContentData() {
      var func = randomFrom([
        function () {
          fnNameA10(target, 'content');
        },
        function () {
          fnNameB20(target, 'content', articleId);
        }
      ]);
      (func)();
    }
    randomContentAd();
  }
};

Do you mean that the function should take in {function:percentage} as input? — sPaz
– sPaz, Commented Dec 3, 2013 at 19:30
Are you asking how to determine the chance that a function will be called given a equal weighting OR are you asking how to weight a functions chance of being called? — Nathaniel Johnson
– Nathaniel Johnson, Commented Dec 3, 2013 at 19:35

sPaz · Accepted Answer · 2013-12-03 20:00:44Z

4

Here is your answer:

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

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

    var random_num = rand(0, total_weight);
    var weight_sum = 0;
    //console.log(random_num)

    for (var i = 0; i < list.length; i++) {
        weight_sum += weight[i];
        weight_sum = +weight_sum.toFixed(2);

        if (random_num <= weight_sum) {
            return list[i];
        }
    }

    // end of function
};

var list = ['javascript', 'php', 'ruby', 'python'];
var weight = [0.5, 0.2, 0.2, 0.1];
var random_item = getRandomItem(list, weight);

answered Dec 3, 2013 at 20:00

sPaz

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4 Comments

Nathaniel Johnson Over a year ago

I liked your original setup sPaz.

sPaz Over a year ago

@Emmentaler I didn't know your answer was accepted already. :P Here, take my upvote...

Steve Over a year ago

@sPaz, in fairness you provided a working solution (in the comments) few seconds before Emmentaler and I promised to accept your answer if you submitted one. Thanks again. :)

Nathaniel Johnson Over a year ago

I think that is fair. I borrowed his start anyway :-)

FelixSFD · Accepted Answer · 2017-08-26 14:51:14Z

3

http://plnkr.co/edit/wzKp8PqNJ4Fmyo2504Cu?p=preview

var funcs = [
  {probability: 20, fn: function(){console.log("20%")}},
  {probability: 10, fn: function(){console.log("10%")}},
  {probability: 70, fn: function(){console.log("70%")}}
];

var total = 0;
var n = Math.random();
for(var i=0; i<funcs.length; ++i) {
  total+=funcs[i].probability;
  if(n*100<total) {
    funcs[i].fn.call(this);
    break;
  }
}

Here I am getting a random number between 0 and 1 then determining where that number falls in array. I do this by stacking the percentages up and comparing the number to the total amount. I need the break because every element in the array will come back true once the condition is met and I only want the first one.

edited Aug 26, 2017 at 14:51

FelixSFD

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answered Dec 3, 2013 at 19:46

Nathaniel Johnson

4,8471 gold badge44 silver badges71 bronze badges

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