Cartesian product

cartesian.js

import { flatten } from 'lodash'
const flatMap = (xs, f) => flatten(xs.map(f))

/**
 * > cartesian([1, 2], [4, 5, 6], [7])
 * [ [ 1, 4, 7 ],
 *   [ 1, 5, 7 ],
 *   [ 1, 6, 7 ],
 *   [ 2, 4, 7 ],
 *   [ 2, 5, 7 ],
 *   [ 2, 6, 7 ] ]
 */

export default function cartesian(...sets) {
  return sets.reduce((product, nextSet) =>
    flatMap(product, set =>
      nextSet.map(item => [...set, item])),
    [[]])
}