add unique function to Array

unique.array.js

//add unique function to Array
Array.prototype.unique = function() {
    var o = {}, i, l = this.length, r = [];
    for(i=0; i<l;i++) o[this[i]] = this[i];
    for(i in o) r.push(o[i]);
    return r;
};
//usage:
// a = "a a bb";
// a =a.split(" ");
// a =a.unique();
// a =a.join(" ");