jquery little bit lazier map / collect method

gistfile1.js

(function($){
  $.collect = function(){
    var selector = arguments[0];
    var fn = arguments[1];
    var arg = arguments[2];
    var collected = [];
    $(selector).each(function(){
      value = arg ? $(this)[fn](arg) : $(this)[fn]();
      collected.push(value);
    });
    return collected;
  };
})(jQuery);

// $.collect('input', 'val');
// $.collect(thing.find('li'), 'data', 'resource-id');

I don't know why $('input').val() returns the value of the first input matched instead of an array of values from the items it matched.