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January 17, 2024 03:27
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Fun with Object.groupBy and Map.groupBy
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| /** | |
| * 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) |
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