docs: protected ArrayDBIDs affectedkNN(List<? extends KNNList> extract, DBIDs remove) {
      HashSetModifiableDBIDs ids = DBIDUtil.newHashSet();
      for(KNNList drps : extract) {
        for(DBIDIter iter = drps.iter(); iter.valid(); iter.advance()) {
          ids.add(iter);
        }
      }
      ids.removeDBIDs(remove);
      // Convert back to array
      return DBIDUtil.newArray(ids);
    }