static Map<S, Int> conceptsCountByDate(S dbID) {
  new TreeMap<S, Int> map;
  for (S dateAndHour, int count : conceptsCountByDateAndHour(dbID)) {
    S date = dropAfterMinus(dateAndHour);
    map.put(data, maxOfInts_possiblyNull(map.get(date), count));
  }
  ret map;
}