code: @Override
    public void writeExternal(ObjectOutput out) throws IOException {
      out.writeInt(DBIDUtil.asInteger(id));
      out.writeInt(values.length);
      for(double v : values) {
        out.writeDouble(v);
      }
    }
docs: Calls the super method and writes the values of this entry to the specified
  stream.
  
  @param out the stream to write the object to
  @throws java.io.IOException Includes any I/O exceptions that may occur