Return from array and never repeat

Question

var randomArray = [
   'a','b', 'c'
];

const randomize = () => {
  let tempArray = randomArray;
  let randomIndex = Math.floor(Math.random()*randomArray.length);
  let randomItem = randomArray[randomIndex];
  
  // remove item
  randomArray.splice(randomIndex, 1);
  
  // return item
  return randomItem;
}

for (let i = 0; i < randomArray.length; i++) {
  console.log(randomize())
}

I'm trying to return items based on the length of the array (3) but for whatever reason I only return (2).

You delete items from the array as you loop through it. Therefore its `.length` changes. There fore when `i = 2` and `randomArray.length = 1` the condition stops the loop. — VLAZ, Feb 24 '22 at 21:50
Check out https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Math/random — Eli Richardson, Feb 24 '22 at 21:51
Just shuffle your array, then your items will be randomly ordered. — Heretic Monkey, Feb 24 '22 at 21:52

score 1 · Accepted Answer · answered Feb 24 '22 at 21:51

As the size of the array is reduced, you shouldn't also increment i. As both its length and i move with a step, you are ending the loop too soon. You just want to check the length:

var randomArray = [
   'a','b', 'c'
];

const randomize = () => {
  let randomIndex = Math.floor(Math.random()*randomArray.length);
  let randomItem = randomArray[randomIndex];
  
  // remove item
  randomArray.splice(randomIndex, 1);
  
  // return item
  return randomItem;
}

while (randomArray.length) {
  console.log(randomize())
}

Not your question, but note that splice returns the slice that was "spliced" out of the array, so you can use that instead of assigning the value to a variable:

var randomArray = [
   'a','b', 'c'
];

const randomize = () => {
  let randomIndex = Math.floor(Math.random()*randomArray.length);
  // remove & return the item
  return randomArray.splice(randomIndex, 1)[0];
}

while (randomArray.length) {
  console.log(randomize())
}

love this solution... thank you. I never knew the for loop would read the length as it went along... but knew how the for loop worked with i variable lol. — Tom, Feb 24 '22 at 21:57

score 0 · Answer 2 · answered Feb 24 '22 at 21:51

You need a diffrerent loop and check just the length of the array.

var randomArray = ['a','b', 'c'];

const randomize = () => {
    const randomIndex = Math.floor(Math.random() * randomArray.length);
    return randomArray.splice(randomIndex, 1)[0];
}

while (randomArray.length) {
    console.log(randomize())
}

score 0 · Answer 3 · answered Feb 24 '22 at 21:52

You are removing the item from the list when you call randomize(), therefore your code only runs twice. Instead, you could use a copy of the array in your randomize() function. We can do this with the .slice() method. This will allow us to preserve the values of randomArray:

var randomArray = [
   'a','b', 'c'
];
let tempArray = randomArray.slice();

const randomize = () => {
  let randomIndex = Math.floor(Math.random()*tempArray.length);
  let randomItem = tempArray[randomIndex];
  
  // remove item
  tempArray.splice(randomIndex, 1);
  
  // return item
  return randomItem;
}

for (let i = 0; i < randomArray.length; i++) {
  console.log(randomize());
}

score 0 · Answer 4 · answered Feb 24 '22 at 21:52

var randomArray = [
   'a','b', 'c'
];
var count = randomArray.length;
const randomize = () => {
  let tempArray = randomArray;
  let randomIndex = Math.floor(Math.random()*randomArray.length);
  let randomItem = randomArray[randomIndex];
  
  // remove item
  randomArray.splice(randomIndex, 1);
  
  // return item
  return randomItem;
}

for (let i = 0; i < count; i++) {
  console.log(randomize())
}

Return from array and never repeat

4 Answers4