Transform Array of Array => Horizontal to Vertical

Horizontal2Vertical.js

const arr = [
  [1, 2, 3],
  [4, 5, 6],
  [7, 8, 9]
];

const rotate = arr.reduce((value, row) => {
  return row.map((_, i) => {
    return [...(value[i] || []), row[i]];
  });
}, []);

console.log(rotate);
/*
[
  [1, 4, 7],
  [2, 5, 8],
  [3, 6, 9]
]
*/