The missing counterpart of jQuery.map()

jquery.reduce.js

/* jQuery core team does not want to add 'reduce' -
 * Details: http://dev.jquery.com/ticket/1886
 */
(function($) {

  $.reduce = function(array, callback, initialValue) {
    if (Array.prototype.reduce) {
      return Array.prototype.reduce.call(array, callback, initialValue);
    }

    $.each(array, function(index, elem) {
      initialValue = callback.call(null, initialValue, elem, index, array);
    });

    return initialValue;
  };

  $.fn.extend({
    reduce: function(callback, initialValue) {
      return $.reduce(this, callback, initialValue);
    }
  });

})(jQuery);