Cross product of 2 javascript arrays

crossProduct.js

const {equals, flatten, join, map, pipe, unnest, xprod} = require('ramda');
const xprod2 = require('./xprod.js');

const urls = [
  'stackexchange.com',
  'askubuntu.com',
  'superuser.com'
];

const filters = [
  '###sidebar',
  '###left-sidebar',
  '###overlay-header',
  '##.site-footer--container',
  '##.js-review-button',
  '##.top-bar'
]

const createFilters = pipe(xprod, map(join('')), unnest);
const createFilters2 = pipe(xprod2, map(join('')), unnest);

const res = createFilters(urls, filters);
const res2 = createFilters2(urls, filters);

console.dir(res);
console.dir(res2);

require('assert')(equals(res, res2));

xprod.js

// returns an array with pairs representing the cross product of the 2 arrays
// xprod([1,2,3], [4,5,6]) === [[1,4],[2,5],[3,6]];

export default (a, b) => {
  var result = [];
  for (const i of a) {
    for (const j of b) {
      result.push([i, j]);
    }
  }
  return result;
}

To dedupe the results (i.e., [1,2,3] X [1,2,3] and you do not want [1,1] in the results, you can do it a few different ways:

change result.push([i, j]) to if (i !== j) result.push([i, j])

Or

Leave the implementation as-is and just filter the result (if it is small enough to iterate over every pair without too much performance loss):

const result = xprod([1,2,3],[1,2,3]);
const dedupedResult = xprod.filter([a,b] => a === b);