javascript中多个对象数组上的笛卡尔积

Question

I have been working on cartesian product for single elements and array of objects. For single array elements I have understood the solution but for array of objects I struggle to achieve. For example input

cartesianProductOf([{col1:'A'}], [{col2:'B'},{col3:'C'}]) 

Output :

[{col1:'A',col2:'B'},{col1:'A',col3:'C'}]

Here is the function which I was working on

function cartesianProductOf() {
     return Array.prototype.reduce.call(arguments, function(a, b) {

         var ret = [];
         debugger;

         a.forEach(function(a) {
                 b.forEach(function(b) {
                 var r = a.concat([b])
                 ret.push(r);
             });
         });

         return ret;

    }, [[]]);
}

This function returning this result

[{col1:'A'},{col2:'B'}],[{col1:'A'},{col3:'C'}]

Need guidance.

Answer 1

Instead of using an array to push to, you want to merge the objects:

function cartesianProductOf() {
     return Array.prototype.reduce.call(arguments, function(a, b) {
         var ret = [];
         a.forEach(function(a_el) {
             b.forEach(function(b_el) {
                 ret.push(Object.assign({}, a_el, b_el));
//                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
             });
         });
         return ret;
    }, [{}]);
//      ^^
}

If you don't want to use Object.assign or it's polyfill, the equivalent would be

                 var r = {};
                 for (var p in a_el)
                     r[p] = a_el[p];
                 for (var p in b_el)
                     r[p] = b_el[p];
                 ret.push(r);

Answer 2

Here's a solution using Ramda.js

 const cartesianProduct = (...Xs) => R.reduce( (Ys, X) => R.map(R.apply(R.append), R.xprod(X, Ys)), [[]], Xs ) const cartesianProductOf = (...objs) => R.map(R.mergeAll, cartesianProduct(...objs)) console.log( cartesianProductOf( [{col1: 'A'}],[{col2: 'B'}, {col3: 'C'}], ) ) 

 <script src="//cdnjs.cloudflare.com/ajax/libs/ramda/0.25.0/ramda.min.js"></script>