StringPiece DenseTensorColumn<StringPiece>::Feature(int64 batch, int64 n,
                                                    bool strong_hash) const {
  return tensor_.matrix<tstring>()(batch, n);
}
StringPiece DenseTensorColumn<StringPiece>::Feature(int64 batch, int64 n,
                                                    bool strong_hash) const {
  return tensor_.matrix<tstring>()(batch, n);
}