tstring SparseTensorColumn<tstring>::Feature(int64 batch, int64 n,
                                             bool strong_hash) const {
  const int64 start = feature_start_indices_[batch];
  if (DT_STRING == values_.dtype())
    return values_.vec<tstring>().data()[start + n];
  return std::to_string(values_.vec<int64>().data()[start + n]);
}
tstring SparseTensorColumn<tstring>::Feature(int64 batch, int64 n,
                                             bool strong_hash) const {
  const int64 start = feature_start_indices_[batch];
  if (DT_STRING == values_.dtype())
    return values_.vec<tstring>().data()[start + n];
  return std::to_string(values_.vec<int64>().data()[start + n]);
}