Javascript algorithm to find elements in array that are not in another array

Question

I\'m looking for a good algorithm to get all the elements in one array that are not elements in another array. So given these arrays:

var x = [\"a\",\"b\",\         


        

Answer 1

This is a late answer, but it uses no libraries so some may find it helpful.

/**
 * Returns a non-destructive Array of elements that are not found in
 * any of the parameter arrays.
 *
 * @param {...Array} var_args   Arrays to compare.
 */
Array.prototype.uniqueFrom = function() {
  if (!arguments.length)
    return [];
  var a1 = this.slice(0); // Start with a copy

  for (var n=0; n < arguments.length; n++) {
    var a2 = arguments[n];
    if (!(a2 instanceof Array))
      throw new TypeError( 'argument ['+n+'] must be Array' );

    for(var i=0; i<a2.length; i++) {
      var index = a1.indexOf(a2[i]);
      if (index > -1) {
        a1.splice(index, 1);
      } 
    }
  }
  return a1;
}

Example:

var sheetUsers = ['joe@example.com','fred@example.com','sam@example.com'];
var siteViewers = ['joe@example.com','fred@example.com','lucy@example.com'];
var viewersToAdd = sheetUsers.uniqueFrom(siteViewers);  // [sam@example.com]
var viewersToRemove = siteViewers.uniqueFrom(sheetUsers);  // [lucy@example.com]

Answer 2

Here's an alternative using underscore.js:

function inAButNotInB(A, B) {
  return _.filter(A, function (a) {
    return !_.contains(B, a);
  });
}