Get all the combinations of 3d array in js-CodePudding

I'm trying to get all the possible combinations of a 3d array. I found a lot of answers for one- or two-dimensional arrays with recursive functions but no solution works for a deeper nested array.

The array structure is always the same (three levels), but the length of each level can change.

example code:

function getCombinations(arr){
  ...
}

var arr = [[[100, 200]], [[10, 20], [30, 40]]];
var arr2 = [[[100, 200]], [[10, 20], [50]], [[400, 500, 600]]];


res = getCombinations(arr);
res2 = getCombinations(arr2);

expected outputs:

// arr: [[[100, 200]], [[10, 20], [30, 40]]]
[
    [[100], [10, 30]],
    [[100], [10, 40]],

    [[100], [20, 30]],
    [[100], [20, 40]],

    [[200], [10, 30]],
    [[200], [10, 40]],

    [[200], [20, 30]],
    [[200], [20, 40]],
];

// arr2: [[[100, 200]], [[10, 20], [50]], [[400, 500, 600]]]
[
    [[100], [10, 50], [400]],
    [[100], [10, 50], [500]],
    [[100], [10, 50], [600]],

    [[100], [20, 50], [400]],
    [[100], [20, 50], [500]],
    [[100], [20, 50], [600]],

    [[200], [10, 50], [400]],
    [[200], [10, 50], [500]],
    [[200], [10, 50], [600]],

    [[200], [20, 50], [400]],
    [[200], [20, 50], [500]],
    [[200], [20, 50], [600]],
];

CodePudding user response：

By researching Cartesian product function, I get more knowledge to implement a solution

Certesion product function (answered by viebel at this question: Cartesian product of multiple arrays in JavaScript):

function cartesianProduct(arr) {
    return arr.reduce(function (a, b) {
        return a.map(function (x) {
            return b.map(function (y) {
                return x.concat([y]);
            });
        }).reduce(function (a, b) {
            return a.concat(b);
        }, []);
    }, [[]]);
}

Nested call for deeper nested arrays:

let arr = [[[100, 200]], [[10, 20], [30, 40]]];
let res = cartesianProduct(arr.map(a => cartesianProduct(a)));

Thanks a lot to Scott Sauyet for the hint in the comments!

CodePudding user response：

My own version was similar, although I think my cartesian function is a bit simpler.

const cartesian = ([xs, ...xss]) =>
  xs == undefined ? [[]] : xs .flatMap (x => cartesian (xss) .map (ys => [x, ...ys]))

const getCombinations = (xss) => 
  cartesian (xss .map (cartesian))


const arr = [[[100, 200]], [[10, 20], [30, 40]]];
const arr2 = [[[100, 200]], [[10, 20], [50]], [[400, 500, 600]]];

console .log (JSON .stringify (getCombinations (arr), null, 4))
console .log (JSON .stringify (getCombinations (arr2), null, 4))

.as-console-wrapper {max-height: 100% !important; top: 0}