Cartesian product

cartesian_product.js

function cartesianProduct(sets) {
    return sets.reduce(function(items, nextSequence) {
        return nextSequence.map(function(element) {
            return items.map(function(item) {
                var copyItem = item.slice(0);
                copyItem.push(element);
                return copyItem;
            });
        }).reduce(function(sum, current) {
            return sum.concat(current);
        });
    }, [[]]);
}

/* since javascript doesn't have set, pass a list of lists instead. */
console.log(cartesianProduct([['a', 'b'], [1, 2, 3], ['x']]));
/*
[ [ 'a', 1, 'x' ],
  [ 'b', 1, 'x' ],
  [ 'a', 2, 'x' ],
  [ 'b', 2, 'x' ],
  [ 'a', 3, 'x' ],
  [ 'b', 3, 'x' ] ]
*/