Array Permutations function

Question

I'm trying to get a permutations function to work but it's confusing me.

example dataset:

{
    a: [1,2],
    b: [1,2,3],
    c: [1,2]
}

desired output:

[
    [ 'a-1', 'b-1', 'c-1' ],
    [ 'a-1', 'b-1', 'c-2' ],
    [ 'a-1', 'b-2', 'c-1' ],
    [ 'a-1', 'b-2', 'c-2' ],
    [ 'a-1', 'b-3', 'c-1' ],
    [ 'a-1', 'b-3', 'c-2' ],
    [ 'a-2', 'b-1', 'c-1' ],
    [ 'a-2', 'b-1', 'c-2' ],
    [ 'a-2', 'b-2', 'c-1' ],
    [ 'a-2', 'b-2', 'c-2' ],
    [ 'a-2', 'b-3', 'c-1' ],
    [ 'a-2', 'b-3', 'c-2' ],
]

So far I've iterated over the Object, then iterated over the Array for each key and then need to do that all again..

To start I broke the values out like so:

[
    [ 'a-1', 'a-2' ],
    [ 'b-1', 'b-2', 'b-3' ],
    [ 'c-1', 'c-2' ]
]

then iterated over them:

var list_joined = []
var list = []
array.forEach((key, index) => {
    key.forEach((value) => {
        var tmp = [value]
        array.forEach((_value, _index) => {
            if(_index != index) {
                tmp.push(_value[0])
            }
        })
        tmp = tmp.sort()
        if(list_joined.indexOf(tmp.join('_')) < 0) {
            list_joined.push(tmp.join('_'))
            list.push(tmp)
        }
    })
})

result

[
    [ 'a-1', 'b-1', 'c-1' ],
    [ 'a-1', 'b-1', 'c-2' ],
    [ 'a-1', 'b-2', 'c-1' ],
    [ 'a-1', 'b-3', 'c-1' ],
    [ 'a-2', 'b-1', 'c-1' ]
]

I can't quite put my finger on where to fix the iterative process.

Nina Scholz · Accepted Answer · 2016-09-09 09:54:17Z

2

You could use an iterative and recursive approach for it.

function combine(object) {

    function c(part, index) {
        object[keys[index]].forEach(function (a) {
            var p = part.concat(keys[index] + '-' + a);
            if (p.length === keys.length) {
                r.push(p);
                return;
            }
            c(p, index + 1);
        });
    }

    var keys = Object.keys(object),
        r = [];

    c([], 0);
    return r;
}

var data = { a: [1, 2], b: [1, 2, 3], c: [1, 2] },
    result = combine(data);

console.log(result);

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

answered Sep 9, 2016 at 9:54

Nina Scholz

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2 Comments

8eecf0d2 Over a year ago

Thank you! question: did you just write that free hand or have something similar stashed away?

Nina Scholz Over a year ago

it's part of a canon (of me).

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