Some useful array extensions (dependent on javascript 1.6)

Array.js

Array.prototype.intersect = function(b) {
  return this.filter(function(n) {
    return (b.indexOf(n) != -1);
  });
}

Array.prototype.diff = function(a) {
  return this.filter(function(n) {
    return !(a.indexOf(n) > -1);
  });
}

Array.prototype.unique = function() {
  var a = this.concat();

  for (var i = 0; i < a.length; i++)
    for (var j = i + 1; j < a.length; j++)
      if (a[i] === a[j])
        a.splice(j, 1);

  return a;
}

Array.prototype.union = function(b) {
  return this.concat(b).unique()
}