static Map<S, Int> conceptsCountByDate(S dbID) {
  new TreeMap<S, Int> map;
  for (S dateAndHour, int count : conceptsCountByDateAndHour(dbID)) {
    S date = substring(dateAndHour, 0, 4) + "/" + substring(dateAndHour, 4, 6) + "/" + substring(dateAndHour, 6, 8);
    map.put(date, maxOfInts_possiblyNull(map.get(date), count));
  }
  ret map;
}