An algorithm that divides items from one or more arrays over one or more output arrays, all in a single for-loop

divide-evenly.js

function divideEvenly(arrays, numOutputs) {
  const arraysLength = arrays.length;
  const totalLength = arrays.reduce((amount, pool) => amount + pool.length, 0);
  const result = [];

  let pool, item, column;
  for (let i = 0; i < totalLength; i++) {
    pool = arrays[i % arraysLength];
    item = pool[Math.floor(i / arraysLength)];
    column = Math.floor(i / (totalLength / numOutputs));
    if (result.length <= column) result.push([]);
    result[column].push(item);
  }
  return result;
}

// ---- tests ----

const numbers = [1, 2, 3, 4, 5, 6];
const chars = ['a', 'b', 'c', 'd', 'e', 'f'];
const exes = ['x1', 'x2', 'x3', 'x4', 'x5', 'x6'];

console.log(divideEvenly([numbers, chars, exes], 3));
// [1, "a", "x1", 2, "b", "x2"]
// [3, "c", "x3", 4, "d", "x4"]
// [5, "e", "x5", 6, "f", "x6"]

console.log(divideEvenly([numbers, chars, exes], 6));
// [1, "a", "x1"]
// [2, "b", "x2"]
// [3, "c", "x3"]
// [4, "d", "x4"]
// [5, "e", "x5"]
// [6, "f", "x6"]

console.log(divideEvenly([numbers], 3));
// [1, 2]
// [3, 4]
// [5, 6]

console.log(divideEvenly([numbers], 2));
// [1, 2, 3]
// [4, 5, 6]