zipWithReduce.js

// An simple zip function with reduce()

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

const zip = arr => {
  //loop through outter array
  return arr.reduce(function(outter, inner) {
    // loop through inner arrays
    inner.forEach(function(num, i) {
      // check if there is an array to add zipped values to
      if (outter[i] === undefined) {
        // if not, will create a new one
        let newArr = [];
        newArr.push(num);
        outter.push(newArr)
      } else {
        // if there exists an array, will add to it
        outter[i].push(num)
      }
    })
    return outter
    // set initial value of reduce to an empty array
  }, [])
}

console.log(zip(example)) // [ [ 1, 4, 7 ], [ 2, 5, 8 ], [ 3, 6, 9 ] ]