Shuffle nested arrays in Javascript

May 13, 2022

I’m trying to sort multiple arrays within an array (which also has to be shuffled). A simplified example is:

let toShuffle = [
[1, 2, 3, 4, 5],
[9, 8, 7, 6, 5],
[10, 67, 19 ,27]
...
];

const shuffled = shuffle(toShuffle);

// outout would look something like:
// [
//   [8, 6, 5, 7, 9],
//   [4, 3, 1, 5, 2],
//   [19, 26, 10, 67],
//   ...
// ]

This needs to be flexible, so any number of arrays with any amount of values should be valid.

Here is what I’ve tried:

function shuffle(a) {
  for (let e in a) {
    if (Array.isArray(a[e])) {
      a[e] = shuffle(a[e]);
    } else {
      a.splice(e, 1);
      a.splice(Math.floor(Math.random() * a.length), 0, a[e]);
    }
  }

  return a;
}

console.log("Shuffled: " + shuffle([
  [1, 2, 3, 4, 5],
  [5, 4, 3, 2, 1]
]))

But it’s not working as intended. Is their an easier way to do this? Or is my code correct and just buggy.

>Solution :

You almost got it. The problem is that you are removing one item from an array, instead of capturing the removed item and them placing in a random position:

let toShuffle = [
[1, 2, 3, 4, 5],
[9, 8, 7, 6, 5],
[10, 67, 19 ,27]
];

function shuffle(a) {
  a = [...a]; //clone array
  for (let e in a) {
    if (Array.isArray(a[e])) {
      a[e] = shuffle(a[e]);
    } else {
      a.splice(~~(Math.random() * a.length), 0, a.splice(e, 1)[0]);
    }
  }

  return a;
}

console.log(JSON.stringify(shuffle(toShuffle)))
console.log(JSON.stringify(toShuffle))

[EDIT]
The original code did not shuffle the parent array, if you need shuffle everything recursively, you can use this:

let toShuffle = [
[1, 2, 3, 4, 5],
[9, 8, 7, 6, 5],
[10, 67, 19 ,27]
];

function shuffle(a) {
  a = a.map(i => Array.isArray(i) ? shuffle(i) : i); //clone array
  a.sort(i => ~~(Math.random() * 2) - 1); //shuffle
  return a;
}

console.log("shuffled", JSON.stringify(shuffle(toShuffle)))
console.log("original", JSON.stringify(toShuffle))