$.fn.extend = function(obj) {
  return this.each(function() {
    for (var prop in obj) this[prop] = obj[prop];
  });
};

$.fn.collect = function(func) {
  var r = [];
  this.each(function(i) { r.push(func.apply(this, [i])); });
  return r;
};

$.fn.select = function(func) {
  var r = [];
  this.each(function(i) { if (func.apply(this, [i])) r.push(this); });
  return r;
};

$.fn.first = function() { 
  return $(this.get(0)); 
};

$.fn.last = function() { 
  return $(this.get(this.size() - 1)); 
};

$.fn.pluck = function(prop) {
  return this.collect(function() {
    return this[prop];
  });
};