Fun with Object.groupBy and Map.groupBy

zip-the-worst-way.js

/**
 * This is a fun attempt to implement a `zip` function using the new Object.groupBy and Map.groupBy functions because I hate index math.
 */

/**
 * A silly implementation of zip using [Object.groupBy](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/groupBy).
 * 
 * It's zip! Great explanation here of the Python implementation (which is better than this one)
 * @see https://docs.python.org/3.3/library/functions.html#zip
 * 
 * @param {...any[]} lists Your arrays to zip
 * @returns {[...any[]]} An array where the i-th element contains all of the i-th elements from the given arrays 
 * 
 * @remarks
 * This implementation is just for fun. Pick some better implementation for your production application like [itertools-ts](https://www.npmjs.com/package/itertools-ts).
 */
const zip = (...lists) => Array.from(
  Object.values(
    Object.groupBy(
      lists.flatMap(list => [...list.entries()]),
      ([index]) => index
    )
  ),
  group => group.map(([, value]) => value)
)

/**
 * The same as {@link zip} but using [Map.groupBy](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map/groupBy).
 * 
 * @param {...any[]} lists Your arrays to zip
 * @returns {[...any[]]} An array where the i-th element contains all of the i-th elements from the given arrays 
 */
const zipWithMap = (...lists) => Array.from(
  Map.groupBy(
    lists.flatMap(list => [...list.entries()]),
    ([ index ]) => index
  ).values(),
  group => group.map(([ , value ]) => value)
)

const simpleLists = [
  ['a', 'b', 'c'],
  ['d', 'e', 'f'],
]

/**
 * Example 1
 * 
 * Returns:
 * ```js
 * [
 *	["a","d"],
 *	["b","e"],
 *	["c","f"]
 * ]
 * ```
 * 
 * Step by Step:
 * const entries = lists.flatMap(list => [...list.entries()]) // [[0, "a"], [1, "b"], [2, "c"], [0, "d"], [1, "e"], [2, "f"]]
 * const groups = Object.groupBy(entries, ([index]) => index) // { 0: [[0, "a"], [0, "d"]], 1: [[1, "b"], [1, "d"]], 2: [[2, "c"], [2, "f"]] }
 * const groupsAsArray = Object.values(groups) // [[[0, "a"], [0, "d"]], [[1, "b"], [1, "d"]], [[2, "c"], [2, "f"]]]
 * Array.from(groupsAsArray, group => group.map(([, value]) => value)) // [["a", "d"], ["b", "d"], ["c", "f"]]
 */
zip(simpleLists)

const lists = [
  ['a', 'b', 'c'],
  ['d', 'e', 'f', 'g', 'h'],
  ['i'],
  ['j', 'k', 'k']
]

/**
 * Example 2
 * 
 * Returns:
 * ```js
 * [
 *   ["a", "d", "i", "j"],
 *   ["b", "e", "k"],
 *   ["c", "f", "k"],
 *   ["g"],
 *   ["h"]
 * ]
 * ```
 */
zipWithMap(lists)