Cartesian product of javascript object properties

Question

I have an object of the following form (simplified test case below)

var test = {
        shirts: {
            sizes: ['large', 'medium']
            ,colors:['red', 'blue']
        }
        , trousers: {
            type: ['formal', 'casual']
            , pattern: ['plaid', 'stripes']
        }
    };

I want to generate a cartesian product of the properties so that the output is an array of the following form:

// desired output

[ {shirts:{sizes:'large', color:'red'}, trousers:{type:'formal', pattern:'plaid'}}
  ,{shirts:{sizes:'large', color:'red'}, trousers:{type:'formal', pattern:'stripes'}}
  ,{shirts:{sizes:'large', color:'red'}, trousers:{type:'casual', pattern:'plaid'}}
  , {shirts:{sizes:'large', color:'red'}, trousers:{type:'casual', pattern:'stripes'}}
  ,{shirts:{sizes:'large', color:'blue'}, trousers:{type:'formal', pattern:'plaid'}}
..... and so on  ]

How can I achieve this? I worked up the following code (based on a modification of code for cartesian product of array from another SO post) but I seem to be tying myself in knots trying to get this to work.

 function myCartesianProduct(input, current) {
    if (!input) { return []; }


    var head = input[Object.keys(input)[0]];

    var tail = objSlice(input);

    var output = [];


    for (var key in head) {

        for (var i = 0; i < head[key].length; i++) {

            var newCurrent = copy(current);

            newCurrent[key] = head[key][i];


            if (Object.keys(tail).length) {   //if tail.length
                var productOfTail =
                        myCartesianProduct(tail, newCurrent);
                output = output.concat(productOfTail);

            } else {
                output.push(newCurrent);

            }
        }
    }
    return output;
}


function objSlice(obj) {
    var slicedObj = angular.copy(obj);  // copy object using angularJs copy method
    delete slicedObj[Object.keys(slicedObj)[0]]; //delete the first key
    return slicedObj;
};

function copy(obj) {
        var res = {};
        for (var p in obj) res[p] = obj[p];
        return res;
    }

console.log(myCartesianProduct(test));

Thanks in advance for your help with this!

@Paul, this case is different. I did see the other posts on this (and created the code based on a modification), but there is a difference in that in this case, we have nested object properties as opposed to array of arrays. — Jarnal
– Jarnal, Commented Nov 2, 2014 at 9:24
Yes, I was thinking perhaps you could combine Object.keys() on sub-objects with the function for cartesian product of arrays in the other question, and then restructure the output from an array of arrays to an array of objects, with, say map — Paul
– Paul, Commented Nov 2, 2014 at 9:27

georg · Accepted Answer · 2014-11-02 09:56:55Z

Ok, let's start with a function that generates a product of given arrays:

function product(args) {
    if(!args.length)
        return [[]];
    var prod = product(args.slice(1)), r = [];
    args[0].forEach(function(x) {
        prod.forEach(function(p) {
            r.push([x].concat(p));
        });
    });
    return r;
}

The next one uses product to convert something like {a:[1,2], b:[3,4]} into [{a:1,b:3},{a:1,b:4},{a:2,b:3},{a:2,b:4}]:

function objectProduct(obj) {
    var keys = Object.keys(obj),
        values = keys.map(function(x) { return obj[x] });

    return product(values).map(function(p) {
        var e = {};
        keys.forEach(function(k, n) { e[k] = p[n] });
        return e;
    });
}

For your test data, you have to apply it twice:

var result = {};
Object.keys(test).forEach(function(k) {
    result[k] = objectProduct(test[k])
});

result = objectProduct(result);

This gives you the output you wanted.

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