Javascript equivalent of Python's zip function

Question

Is there a javascript equivalent of Python\'s zip function? That is, given multiple arrays of equal lengths create an array of pairs.

For instance, if I have three

Answer 1

In addition to ninjagecko's excellent and comprehensive answer, all it takes to zip two JS-arrays into a "tuple-mimic" is:

//Arrays: aIn, aOut
Array.prototype.map.call( aIn, function(e,i){return [e, aOut[i]];})

Explanation:
Since Javascript doesn't have a tuples type, functions for tuples, lists and sets wasn't a high priority in the language specification.
Otherwise, similar behavior is accessible in a straightforward manner via Array map in JS >1.6. (map is actually often implemented by JS engine makers in many >JS 1.4 engines, despite not specified).
The major difference to Python's zip, izip,... results from map's functional style, since map requires a function-argument. Additionally it is a function of the Array-instance. One may use Array.prototype.map instead, if an extra declaration for the input is an issue.

Example:

_tarrin = [0..constructor, function(){}, false, undefined, '', 100, 123.324,
         2343243243242343242354365476453654625345345, 'sdf23423dsfsdf',
         'sdf2324.234dfs','234,234fsf','100,100','100.100']
_parseInt = function(i){return parseInt(i);}
_tarrout = _tarrin.map(_parseInt)
_tarrin.map(function(e,i,a){return [e, _tarrout[i]]})

Result:

//'('+_tarrin.map(function(e,i,a){return [e, _tarrout[i]]}).join('),\n(')+')'
>>
(function Number() { [native code] },NaN),
(function (){},NaN),
(false,NaN),
(,NaN),
(,NaN),
(100,100),
(123.324,123),
(2.3432432432423434e+42,2),
(sdf23423dsfsdf,NaN),
(sdf2324.234dfs,NaN),
(234,234fsf,234),
(100,100,100),
(100.100,100)

Related Performance:

Using map over for-loops:

See: What is the most efficient way of merging [1,2] and [7,8] into [[1,7], [2,8]]

Note: the base types such as false and undefined do not posess a prototypal object-hierarchy and thus do not expose a toString function. Hence these are shown as empty in the output.
As parseInt's second argument is the base/number radix, to which to convert the number to, and since map passes the index as the second argument to its argument-function, a wrapper function is used.

Answer 2

Along other Python-like functions, pythonic offers a zip function, with the extra benefit of returning a lazy evaluated Iterator, similar to the behaviour of its Python counterpart:

import {zip, zipLongest} from 'pythonic';

const arr1 = ['a', 'b'];
const arr2 = ['c', 'd', 'e'];
for (const [first, second] of zip(arr1, arr2))
    console.log(`first: ${first}, second: ${second}`);
// first: a, second: c
// first: b, second: d

for (const [first, second] of zipLongest(arr1, arr2))
    console.log(`first: ${first}, second: ${second}`);
// first: a, second: c
// first: b, second: d
// first: undefined, second: e

// unzip
const [arrayFirst, arraySecond] = [...zip(...zip(arr1, arr2))];

Disclosure I'm author and maintainer of Pythonic

Answer 3

I modified flm's nifty answer to take an arbitrary number of arrays:

function* zip(arrays, i = 0) {
  while (arrays[0][i]) {
    yield arrays.map((arr, j) => arr[j < arrays.length - 1 ? i : i++])
  }
 }

Answer 4

The Mochikit library provides this and many other Python-like functions. developer of Mochikit is also a Python fan, so it has the general style of Python, and also the wraps the async calls in a twisted-like framework.

Answer 5

This shaves a line off Ddi's iterator-based answer:

function* zip(...toZip) {
  const iterators = toZip.map((arg) => arg[Symbol.iterator]());
  const next = () => toZip = iterators.map((iter) => iter.next());
  while (next().every((item) => !item.done)) {
    yield toZip.map((item) => item.value);
  }
}

Answer 6

The Python has two functions: zip and itertools.zip_longest. Implementation on JS/ES6 is like this:

Implementation Python`s zip on JS/ES6

const zip = (...arrays) => {
    const length = Math.min(...arrays.map(arr => arr.length));
    return Array.from({ length }, (value, index) => arrays.map((array => array[index])));
};

Results:

console.log(zip(
    [1, 2, 3, 'a'],
    [667, false, -378, '337'],
    [111],
    [11, 221]
));

[ [ 1, 667, 111, 11 ] ]

console.log(zip(
    [1, 2, 3, 'a'],
    [667, false, -378, '337'],
    [111, 212, 323, 433, '1111']
));

[ [ 1, 667, 111 ], [ 2, false, 212 ], [ 3, -378, 323 ], [ 'a', '337', 433 ] ]

console.log(zip(
    [1, 2, 3, 'a'],
    [667, false, -378, '337'],
    [111],
    []
));

[]

Implementation Python`s zip_longest on JS/ES6

(https://docs.python.org/3.5/library/itertools.html?highlight=zip_longest#itertools.zip_longest)

const zipLongest = (placeholder = undefined, ...arrays) => {
    const length = Math.max(...arrays.map(arr => arr.length));
    return Array.from(
        { length }, (value, index) => arrays.map(
            array => array.length - 1 >= index ? array[index] : placeholder
        )
    );
};

Results:

console.log(zipLongest(
    undefined,
    [1, 2, 3, 'a'],
    [667, false, -378, '337'],
    [111],
    []
));

[ [ 1, 667, 111, undefined ], [ 2, false, undefined, undefined ],
[ 3, -378, undefined, undefined ], [ 'a', '337', undefined, undefined ] ]

console.log(zipLongest(
    null,
    [1, 2, 3, 'a'],
    [667, false, -378, '337'],
    [111],
    []
));

[ [ 1, 667, 111, null ], [ 2, false, null, null ], [ 3, -378, null, null ], [ 'a', '337', null, null ] ]

console.log(zipLongest(
    'Is None',
    [1, 2, 3, 'a'],
    [667, false, -378, '337'],
    [111],
    []
));

[ [ 1, 667, 111, 'Is None' ], [ 2, false, 'Is None', 'Is None' ],
[ 3, -378, 'Is None', 'Is None' ], [ 'a', '337', 'Is None', 'Is None' ] ]