Assign "frequency of output" to an array's elements, using javascript

Question

I have an array like so:

var arrA = [1lemon, 2lemons, 3lemons, 1orange, 2oranges, 3oranges, 1apple, 2apples, 3apples, 1banana, 2bananas, 3bananas, 1coconut, 2coconuts, 3coconuts];

...that I am shuffling with this function:

        function shuffle(array) {
          var currentIndex = array.length, temporaryValue, randomIndex;

          // While there remain elements to shuffle...
          while (0 !== currentIndex) {

            // Pick a remaining element...
            randomIndex = Math.floor(Math.random() * currentIndex);
            currentIndex -= 1;

            // And swap it with the current element.
            temporaryValue = array[currentIndex];
            array[currentIndex] = array[randomIndex];
            array[randomIndex] = temporaryValue;
          }

          return array;
        }

arrA = shuffle(arrA);

...and then I have some code to output the randomized array's fruits, one at a time, and every 4 seconds, like so:

var text = arrA;
var counter = 0;
var elem = document.getElementById("changeText");
setInterval(change, 4000);
function change() {
 elem.innerHTML = text[counter];
    counter++;
    if(counter >= text.length) { counter = 0; }
}

They will appear on a div:

<div id="changeText"><p>pick fruit(s)</p></div>

But in this manner all elements in the array will appear on each loop (they have 100% of possibilities of appearing).

How to do so they appear with a certain frequency?

So the 1fruit appear 50% of the time, the 2fruits 30% of the time, and the 3fruits 20% of the time?

Just wrapping my mind around this...

Thanks for your ideas,

Nina Scholz · Accepted Answer · 2017-02-20 14:36:36Z

1

I suggest to use a continuous check of the probability and the rest of the random number.

This function sets first the return value to the last possible index and iterates until the rest of the random value is smaller than the actual probability.

The probabilities have to sum to one.

function getRandomIndexByProbability(probabilities) {
    var r = Math.random(),
        index = probabilities.length - 1;

    probabilities.some(function (probability, i) {
        if (r < probability) {
            index = i;
            return true;
        }
        r -= probability;
    });
    return index;
}

function getPlural(number, word) {
    return number === 1 ? word : word + 's';
}


var i,
    fruits = ['lemon', 'orange', 'apple', 'banana', 'coconut'],
    probabilities = [0.5, 0.3, 0.2],
    count = {},
    fruit,
    value;

fruits.forEach(function (a) { 
    var i;
    for (i = 1; i <= 3; i++) {
        count[i + getPlural(i, a)] = 0;
    }
});

for (i = 0; i < 1e6; i++) {
    fruit = fruits[Math.floor(Math.random() * fruits.length)];
    value = getRandomIndexByProbability(probabilities) + 1;
    count[value + getPlural(value, fruit)]++;
}

console.log(count);

.as-console-wrapper { max-height: 100% !important; top: 0; }

edited Feb 20, 2017 at 14:36

answered Feb 20, 2017 at 12:27

Nina Scholz

388k26 gold badges367 silver badges417 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Peanuts Over a year ago

Amazing, thanks! Will have to dig into the code to fully get it, but it looks brilliant.

Collectives™ on Stack Overflow

Assign "frequency of output" to an array's elements, using javascript

1 Answer 1

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related