Question 54608 in Javascript Question posted in
A very good W3school tutorial can be found here.

In JavaScript, how to get a set of random integers within a specific range, without any duplicates in the set?

Is there any way to generate random number within a range? I’m making a shuffle function for my audio player using React. I got my song.id works well. Once a random number is "used" I don’t want it again.

But I want to randomly generate a number start with 0 and end with 51 (it can generate 0 and 51). I tried these but I keep getting dupes:

Math.floor(Math.random() * 52))
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3

Answers


  1. 0

    I am also bulid feature like this recently .

    const usedIndexEntries = []; // array for recording utilised indexes

function getRandomIndex() {
  let randomIndex = Math.floor(Math.random() * 52);
  if(usedIndexEntries.length == 52){
    usedIndexEntries = [];
  }
  while (usedIndexEntries.includes(randomIndex)) { // check if the index has already used
    randomIndex = Math.floor(Math.random() * 52); // generate a new random index if it has
  }
  usedIndexEntries.push(randomIndex); // add the index to the array of used indexes
  return randomIndex;
}

    Here I am generating Random Index .If it is already used then it will regenerate till a unique index is found and when it reach at max level then we will empty the array and this process start again.

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  2. 0

    Here’s an example using the array shuffling technique.

    // shuffle swiped from https://stackoverflow.com/a/2450976
function shuffle(array) {
  let currentIndex = array.length,  randomIndex;

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

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

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

  return array;
}

// build an array containing 0-51
const arr = [];
for (let i = 0; i < 52; i++) arr.push(i);

shuffle(arr);

// use arr.shift() to get the next song id
console.log("first song is " + arr.shift());
console.log("second song is " + arr.shift());
console.log("third song is " + arr.shift());
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  3. 0

    Here is a manner to get a list of random numbers for a playlist (same code for an Array of 52 indexes):

        let originalArray=[0, 1, 2, 3, 4];
    let arrayLength = originalArray.length;
    let playlist;
    let rndVal;
    let removed;
    
    function generatePlaylist(){
        playlist = [];
            for( var i = 0; i<arrayLength; i++){
                rndVal = Math.floor(Math.random() * originalArray.length);
                removed = originalArray.splice(rndVal,1);
                playlist.push(removed);
                console.log("value = " + rndVal + " Array = " + originalArray + " removed = " + removed);
            }
        return playlist;
    }
    console.log ("playlist = " + generatePlaylist());

    Edit : More reusable :

        let originalArray=[0, 1, 2, 3, 4];
    let arrayLength;
    let playlist;
    let rndVal;
    let removed;
    
    function generatePlaylist(arrayNum){
        playlist = [];
        arrayLength = arrayNum.length;
            for( var i = 0; i<arrayLength; i++){
                rndVal = Math.floor(Math.random() * arrayNum.length);
                removed = arrayNum.splice(rndVal,1);
                playlist.push(removed);
                console.log("value = " + rndVal + " Array = " + arrayNum + " removed = " + removed);
            }
        return playlist;
    }
    
    console.log ("playlist = " + generatePlaylist(originalArray));
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