Ungroup array elements based on function

OSCC · JavaScript, Array · Jan 23, 2022

Creates an array of elements, ungrouping the elements in an array produced by zip and applying the provided function.

• Use Math.max() and the spread operator (...) to get the longest subarray in the array, Array.prototype.map() to make each element an array.
• Use Array.prototype.reduce() and Array.prototype.forEach() to map grouped values to individual arrays.
• Use Array.prototype.map() and the spread operator (...) to apply fn to each individual group of elements.

const unzipWith = (arr, fn) =>
  arr
    .reduce(
      (acc, val) => (val.forEach((v, i) => acc[i].push(v)), acc),
      Array.from({
        length: Math.max(...arr.map(x => x.length))
      }).map(x => [])
    )
    .map(val => fn(...val));

unzipWith(
  [
    [1, 10, 100],
    [2, 20, 200],
  ],
  (...args) => args.reduce((acc, v) => acc + v, 0)
);
// [3, 30, 300]

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