JQuery - Adding random numbers to an array and then checking if there are repetitions before printing array

Question

I'm trying to write a "for" loop that will go through a list of 30 songs in an array and then print a list of 20 random items in that array with no repetitions.


var items = [];
var songList = [];
var pastSongs = [];

for (i = 1; i <= 30; i++) {
  items.push("song" + i);
}


$(".btn").click(function getRandom() {

  for (g = 1; g <= 20; g++) {

    var randomItem = (items[Math.floor(Math.random() * items.length)]);

    $("h2").text(randomItem);

    songList.push(randomItem);


    if (pastSongs.includes(randomItem)) {
      $("p").text("repeat");
    } else {
      $("p").text(songList);
      (pastSongs).push(randomItem);
    }

  }

});

Just use a shuffle algorithm https://stackoverflow.com/questions/2450954/how-to-randomize-shuffle-a-javascript-array — epascarello, Jan 20 '21 at 20:04
Does this answer your question? [How to efficiently randomly select array item without repeats?](https://stackoverflow.com/questions/17891173/how-to-efficiently-randomly-select-array-item-without-repeats) — Heretic Monkey, Jan 20 '21 at 20:19
Also my answer [Here](https://stackoverflow.com/questions/65768862/random-select-radio-button-from-multiple-radio-group/65768967#65768967) May help — Mohamed-Yousef, Jan 20 '21 at 20:31

score 0 · Answer 1 · answered Jan 20 '21 at 20:16

Check this out on how to shuffle an array: How to randomize (shuffle) a JavaScript array?

And then you can just take the first 20 elements of that array either by popping the last 10 elements or looping through and collecting the first ten elements. This way it will be quicker than randomly choosing enough times and then filtering through the array for duplicates

score 0 · Accepted Answer · answered Jan 20 '21 at 21:20

If I only focus on the question title.

Adding random numbers to an array and then checking if there are repetitions before printing array

Aside the "assumed" use case where the suggested duplicate about "shuffling an existing array" would be quite good. If you want to create an array of unique numbers having an amount length of values between a min and a max, Here is how:

function getArrayOfuniqueRandomNumbers(min, max, amount) {
  let result = [];

  if (amount !== undefined && amount < max - min) {
    while (result.length < amount) {
      let randomNumber = Math.floor(Math.random() * (max - min));
      if (result.indexOf(randomNumber) == -1) {
        result.push(randomNumber);
      }
    }
  }

  return result;
}

// So here, you request an array of 20 numbers between 0 and 30
console.log(getArrayOfuniqueRandomNumbers(0,30,20))

The function will return a non-empty array if the requested amount is possible given the min and max.

There is a condition to avoid an infinite loop of the while. So if the provided arguments do not allow to find the required amount of unique numbers, it will return an empty array.

How it works:

while the amount is not reached, keep on trying to add a new random number.

The numbers are added to the array to be returned only if not already present because of the .indexOf() check.

Do whatever you wish with the returned array.

JQuery - Adding random numbers to an array and then checking if there are repetitions before printing array

2 Answers2