zip-iter

Zip Iter

This library contains two very useful functions that really should be a part of the JS standard library (says the python dev). The functions "zip" and "zip longest" have numerous uses in many aspects of programming.

In this library, these functions can handle any kind of iterable (basically anything that has a Symbol.iterator method).

Both functions are generators. To unpack the result easily, you can use the spread operator ([...zip(...iterables)]) or Array.from(zip(...iterables)).

Install

With yarn:

$ yarn add zip-iter

Or with npm:

$ npm add zip-iter

Example usage

Import:

import { zip, zipLongest } from "zip-iter";

With arrays:

const array1 = [1, 2, 3];
const array2 = ['a', 'b', 'c'];

const zipped = zip(array1, array2);
// outputs [1, 'a'], [2, 'b'], [3, 'c']
const zippedArray = Array.from(zipped);
// outputs [[1, 'a'], [2, 'b'], [3, 'c']]

// array1 and array2 have the same number of elements,
// so zipLongest won't do anything special here.
const zippedLongest = zipLongest(array1, array2);
// outputs [1, 'a'], [2, 'b'], [3, 'c']
const zippedLongestArray = [...zippedLongest];
// outputs [[1, 'a'], [2, 'b'], [3, 'c']]

With strings:

const string1 = 'abcd';
const string2 = 'xyz';

const zipped = zip(string1, string2);
// outputs ['a', 'x'], ['b', 'y'], ['c', 'z']

const zippedLongest = zipLongest(string1, string2);
// outputs ['a', 'x'], ['b', 'y'], ['c', 'z'], ['d', undefined]

With iterable objects like Map and Set:

const myMap = new Map();
myMap.set('a', 1).set('b', 2);
const mySet = new Set();
mySet.add('x').add('y').add('z');

const zipped = zip(myMap, mySet);
// outputs [['a', 1], 'x'], [['b', 2], 'y']

const zippedLongest = zipLongest(myMap, mySet);
// outputs [['a', 1], 'x'], [['b', 2], 'y'], [undefined, 'z']

With iterators directly:

const zipped = zip(myMap.entries(), mySet.entries());
// outputs [['a', 1], 'x'], [['b', 2], 'y']

const zippedLongest = zipLongest(myMap.entries(), mySet.entries());
// outputs [['a', 1], 'x'], [['b', 2], 'y'], [undefined, 'z']

Generators are iterators, so they work too:

const genNumbers = function*(count: number): Generator<number> {
    for (let x = 0; x < count; x++) {
        yield x;
    }
};
const generator1 = genNumbers(3);
const generator2 = genNumbers(2);

const zipped = zip(generator1, generator2);
// outputs [0, 0], [1, 1]

// Generators can't be re-used
const zippedLongest = zipLongest(genNumbers(3), genNumbers(2));
// outputs [0, 0], [1, 1], [2, undefined]

Zips are generators, so they can be zipped too!

const myStr = 'zzz';
const myArr = ['i', 'i', 'i'];
const myMap = new Map().set(0, 'p').set(1, 'p').set(2, 'p');

const zipped1 = zip(myStr, myArr, myMap.values());
const zipped2 = zip(myMap.values(), myArr, myStr);

const zipped3 = zip(zipped1, zipped2);
/**
 * outputs [
 *   [['z', 'i', 'p'], ['p', 'i', 'z']],
 *   [['z', 'i', 'p'], ['p', 'i', 'z']],
 *   [['z', 'i', 'p'], ['p', 'i', 'z']],
 * ]
 */

Acknowledgements

The actual implementation of zip and zipLongest has been taken from the npm package iterablefu, which you can find at the following URL:

https://github.com/toolbuilder/iterablefu

I decided to rip out these functions to make them standalone because the package as a whole comes with some weird, unnecessary dependencies for what should be a relatively straightforward library.

The type declarations for both functions were adapted from the lodash zip implementation. Why not use lodash zip, you ask? Because it only handles arrays and makes no attempt to utilise Symbol.iterator.