code: public function getRequestFilters(Mage_Core_Controller_Request_Http $request)
      {
          if (!$this->requestFilterValues) {
              $filters = $this->getFilterParams();
              $this->requestFilterValues = array();
  
              foreach ($filters as $filter) {
                  $param = $request->getParam($filter, null);
                  if ($param !== null) {
                      $this->requestFilterValues[$filter] = $param;
                  }
              }
          }
  
          return $this->requestFilterValues;
      }
docs: Returns an assoc array with filter and if its value from request.
  Filters missing from request parameters are ignored.
  
  @param Mage_Core_Controller_Request_Http $request
  @return array