Generating all combinations of elements in a single array (for cominations of N elements)

Question

I'm trying to build/find a function, which will give me all combinations for N number of elements.

The solution below gives me an answer for pairs (i.e. 2 elements).

I'd like to parameterize it, so that I can define the number of combined elements (e.g. 3 elements => ['one', 'two', 'three'], ['one', 'two', 'four'], ... , 4 elements, and so on.

(Bonus internet points if you can tell me the name what I'm looking for (cartesian-product?)!)

var array = ['one', 'two', 'three', 'four', 'five'] // get pairs var result = array => array.flatMap((v, i) => array.slice(i+1).map( w => [v, w] )); console.log(result(array)) // output: // [ // ["one", "two"], // ["one", "three"], // ["one", "four"], // ["one", "five"], // ["two", "three"], // ["two", "four"], // ["two", "five"], // ["three", "four"], // ["three", "five"], // ["four", "five"] // ]

Generate subsets of length n or just How to find all subsets of a set in JavaScript? (Powerset of array) and .filter by length. — Sebastian Simon
– Sebastian Simon, Commented Oct 19, 2021 at 3:03

Danilo Mercado Oudalova · Accepted Answer · 2021-10-19 03:07:12Z

I think this is your solution.

/** * Usage Example: * * console.log(combination(['A', 'B', 'C', 'D'], 2, true)); // [[ 'A','A' ], [ 'A', 'B' ]...] (16 items) * console.log(combination(['A', 'B', 'C', 'D'])); // [['A', 'A', 'A', 'B' ],.....,['A'],] (340 items) * console.log(comination(4, 2)); // all posible values [[ 0 ], [ 1 ], [ 2 ], [ 3 ], [ 0, 0 ], [ 0, 1 ], [ 0, 2 ]...] (20 items) */ function combination(item, n) { const filter = typeof n !=='undefined'; n = n ? n : item.length; const result = []; const isArray = item.constructor.name === 'Array'; const pow = (x, n, m = []) => { if (n > 0) { for (var i = 0; i < 4; i++) { const value = pow(x, n - 1, [...m, isArray ? item[i] : i]); result.push(value); } } return m; } pow(isArray ? item.length : item, n); return filter ? result.filter(item => item.length == n) : result; } console.log("#####first sample: ", combination(['A', 'B', 'C', 'D'], 2)); // with filter console.log("#####second sample: ", combination(['A', 'B', 'C', 'D'])); // without filter console.log("#####third sample: ", combination(4, 2)); // just number

Thanks @Danilo, nice answer. One problem, It's showing duplicates... for example: [["A", "A"], ["B", "B"], ["C", "C"]. Were you able to exclude them?
If you could provide some explanation of how your solution works, that'd be great! (e.g. inline comments?)

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