Function groupBy

Groups all values in the iterable under the computed key, based on the keySelector.

Example

const map = groupBy([0, 1, 2, 10, 20, 100, 200], (num) =>
  num.toString().charAt(0)
);
// map → [
//   ['0', [0]],
//   ['1', [1, 10, 100]],
//   ['2', [2, 20, 200]],
// ]