docs: private int updateSizes(DBIDs ids, WritableDataStore<ModifiableDBIDs> labels, WritableIntegerDataStore newSizes) {
      // to count the unclustered all over
      int countUnmerged = 0;
      for(DBIDIter iter = ids.iter(); iter.valid(); iter.advance()) {
        // checking the point's new cluster size after the clustering step
        int newClusterSize = labels.get(iter).size();
        newSizes.putInt(iter, newClusterSize);
        // the point is alone in the cluster --> not merged with other points
        if(newClusterSize == 1) {
          countUnmerged++;
        }
      }
      return countUnmerged;
    }