cartesian/index.js

Computes the cartesian product of arrays provided by an array or an object

var extend = require('xtend/immutable');

// Public API
module.exports = cartesian;

/**
 * Creates cartesian product of the provided properties
 *
 * @param   {object|array} list - list of (array) properties or array of arrays
 * @returns {array} all the combinations of the properties
 */
function cartesian(list)
{
  var last, init, keys, product = [];

  if (Array.isArray(list))
  {
    init = [];
    last = list.length - 1;
  }
  else if (typeof list == 'object' && list !== null)
  {
    init = {};
    keys = Object.keys(list);
    last = keys.length - 1;
  }
  else
  {
    throw new TypeError('Expecting an Array or an Object, but `' + (list === null ? 'null' : typeof list) + '` provided.');
  }

  function add(row, i)
  {
    var j, k, r;

    k = keys ? keys[i] : i;

    // either array or not, not expecting objects here
    Array.isArray(list[k]) || (typeof list[k] == 'undefined' ? list[k] = [] : list[k] = [list[k]]);

    for (j=0; j < list[k].length; j++)
    {
      r = clone(row);
      store(r, list[k][j], k);

      if (i >= last)
      {
        product.push(r);
      }
      else
      {
        add(r, i + 1);
      }
    }
  }

  add(init, 0);

  return product;
}

/**
 * Clones (shallow copy) provided object or array
 *
 * @param   {object|array} obj - object or array to clone
 * @returns {object|array} - shallow copy of the provided object or array
 */
function clone(obj)
{
  return Array.isArray(obj) ? [].concat(obj) : extend(obj);
}

/**
 * Stores provided element in the provided object or array
 *
 * @param   {object|array} obj - object or array to add to
 * @param   {mixed} elem - element to add
 * @param   {string|number} key - object's property key to add to
 * @returns {void}
 */
function store(obj, elem, key)
{
  Array.isArray(obj) ? obj.push(elem) : (obj[key] = elem);
}