public function getStates(\DateTime $start_date, \DateTime $end_date, $reset = TRUE) {
    $events = $this->getEvents($start_date, $end_date, $reset);

    $states = array();
    foreach ($events as $unit => $unit_events) {
      foreach ($unit_events as $event) {
        $states[$unit][$event->getValue()] = $event->getValue();
      }
    }

    return $states;
  }