symmetricDifference.js

// Symmetric Difference
// Create a function that takes two or more arrays and returns an array of the
// symmetric difference (△ or ⊕) of the provided arrays.
//
// Given two sets (for example set A = {1, 2, 3} and set B = {2, 3, 4}), the
// mathematical term "symmetric difference" of two sets is the set of elements
// which are in either of the two sets, but not in both (A △ B = C = {1, 4}). For
// every additional symmetric difference you take (say on a set D = {2, 3}), you
// should get the set with elements which are in either of the two the sets but not
// both (C △ D = {1, 4} △ {2, 3} = {1, 2, 3, 4}).

function sym(args) {
  const argArr = [...arguments];

  const difference = (arr1, arr2) => {
    return arr1.concat(arr2).filter(val => {
      return !arr1.includes(val) || !arr2.includes(val);
    });
  };

  return [...new Set(
    argArr.reduce((acc, curr) => difference(acc, curr))
  )];
}

// Tests:
// sym([1, 2, 3], [5, 2, 1, 4]) should return [3, 4, 5].
// sym([1, 2, 3], [5, 2, 1, 4]) should contain only three elements.
// sym([1, 2, 5], [2, 3, 5], [3, 4, 5]) should return [1, 4, 5]
// sym([1, 2, 5], [2, 3, 5], [3, 4, 5]) should contain only three elements.
// sym([1, 1, 2, 5], [2, 2, 3, 5], [3, 4, 5, 5]) should return [1, 4, 5].
// sym([1, 1, 2, 5], [2, 2, 3, 5], [3, 4, 5, 5]) should contain only three elements.
// sym([3, 3, 3, 2, 5], [2, 1, 5, 7], [3, 4, 6, 6], [1, 2, 3]) should return [2, 3, 4, 6, 7].
// sym([3, 3, 3, 2, 5], [2, 1, 5, 7], [3, 4, 6, 6], [1, 2, 3]) should contain only five elements.
// sym([3, 3, 3, 2, 5], [2, 1, 5, 7], [3, 4, 6, 6], [1, 2, 3], [5, 3, 9, 8], [1]) should return [1, 2, 4, 5, 6, 7, 8, 9].
// sym([3, 3, 3, 2, 5], [2, 1, 5, 7], [3, 4, 6, 6], [1, 2, 3], [5, 3, 9, 8], [1]) should contain only eight elements.