How to get random index in a specific range only once

Question

Hi I would like to get an random index in a specific range of a list. After that the index should not be returned again if I want another random index of a list.

Answer 1

Here is a way to generate random numbers in a [min, max) range and without repetition.

It uses a lookup object to store the values returned so far for each range.

If no number can be returned, it returns undefined.

const usedIndicesByRange = {};

function randomIntInRange(min, max) {
  const key = `${min}-${max}`;
  if (!(key in usedIndicesByRange)) {
    usedIndicesByRange[key] = [];
  }

  if (usedIndicesByRange[key].length === max - min) {
    return undefined;
  }
  
  const getIdx = () => Math.floor(Math.random() * (max - min) + min);
  
  let idx = getIdx();
  while (usedIndicesByRange[key].includes(idx)) {
    idx = getIdx();
  }
  usedIndicesByRange[key].push(idx);
  
  return idx;
}

console.log([...Array(12)].map(() => randomIntInRange(0, 10)));