docs: @Deprecated
    protected final Map<DBID, KNNList> batchNN(N node, DBIDs ids, int kmax) {
      Map<DBID, KNNList> res = new HashMap<>(ids.size());
      for(DBIDIter iter = ids.iter(); iter.valid(); iter.advance()) {
        DBID id = DBIDUtil.deref(iter);
        res.put(id, knnq.getKNNForDBID(id, kmax));
      }
      return res;
    }