code: public static ConcatVectorTable readFromStream(InputStream stream) throws IOException {
          return readFromProto(ConcatVectorTableProto.ConcatVectorTable.parseFrom(stream));
      }
docs: Convenience function to read a factor (assumed serialized with proto) directly from a stream.
  
  @param stream the stream to be read from
  @return a new in-memory feature factor
  @throws IOException passed through from the stream