I'm trying to pick a random element from an array without picking the same element twice.
After a few iterations it is undefined.
It works with return(pick_random_letter()). But WHY?
Why does pick_random_letter() not go back and return later?
let letters = [
{ name: 'A' },
{ name: 'B' },
{ name: 'C' },
{ name: 'D' },
]
let used_letters = [];
function pick_random_letter(){
let random = Math.floor(Math.random() * letters.length);
let next_letter = letters[random].name;
if (used_letters.includes(next_letter)){
if (used_letters.length == letters.length) used_letters = [];
pick_random_letter(); // return(pick_random_letter()) works
}else{
used_letters.push(next_letter);
return next_letter;
}
}
for (let i = 0; i < 4; i++){
let random_letter = pick_random_letter();
console.log(random_letter);
console.log(used_letters);
}Working example:
let letters = [
{ name: 'A' },
{ name: 'B' },
{ name: 'C' },
{ name: 'D' },
]
let used_letters = [];
function pick_random_letter(){
let random = Math.floor(Math.random() * letters.length);
let next_letter = letters[random].name;
if (used_letters.includes(next_letter)){
if (used_letters.length == letters.length) used_letters = [];
return(pick_random_letter());
}else{
used_letters.push(next_letter);
return next_letter;
}
}
for (let i = 0; i < 4; i++){
let random_letter = pick_random_letter();
console.log(random_letter);
console.log(used_letters);
}Thank you
I think you would be better off using a shuffling approach. Create a shuffled list of your letters and pick from these. This avoids any need to check if we've returned a letter previously.
We'd start by creating a shuffledLetters array, then each time we call pick_random_letter() we return the next value.
The shuffle() function here is a basic Fisher–Yates / Knuth shuffle.
function shuffle(arr) {
for (let i = arr.length - 1; i > 0; i--) {
const j = Math.floor(Math.random() * (i + 1));
[arr[i], arr[j]] = [arr[j], arr[i]];
}
return arr;
}
let letters = [
{ name: 'A' },
{ name: 'B' },
{ name: 'C' },
{ name: 'D' },
]
// Create a shuffled copy of the letters array
let shuffledLetters = shuffle([...letters]);
function pick_random_letter() {
return shuffledLetters.pop();
}
for (let i = 0; i < letters.length; i++) {
let random_letter = pick_random_letter();
console.log(random_letter);
}.as-console-wrapper { max-height: 100% !important; }