spudly.shuoink.com

Here’s a prototyped method for Array that computes the symmetric difference between two arrays. It basically returns all the values that are in one or the other array but not both.

Usage:

var setA = [ 1, 2, 3, 4, 5, 6 ];
var setB = [ 4, 5, 6, 7, 8, 9, 10 ];
var diff = setA.difference( setB ); // diff is now [ 1, 2, 3, 7, 8, 9, 10 ]

Array.prototype.difference = function( setB ) {
   var setA = this;

   var setA_seen = {};
   var setB_seen = {};

   for ( var i = 0; i < setB.length; i++ ) {
      setB_seen[ setB[i] ] = true;
   }
   for ( var i = 0; i < setA.length; i++ ) {
      setA_seen[ setA[i] ] = true;
   }

   var difference = [];
   for ( var i = 0; i < setA.length; i++ ) {
      if ( !setB_seen[ setA[i] ] ) {
         difference.push( setA[i] );
      }
   }
   for ( var i = 0; i < setB.length; i++ ) {
      if ( !setA_seen[ setB[i] ] ) {
         difference.push( setB[i] );
      }
   }
   return difference;
};