StringPiece KeyedSparseTensorColumn<StringPiece>::Feature(
    int64 batch, int64 n, bool strong_hash) const {
  const int64 start = feature_start_indices_[batch];
  return values_.vec<tstring>().data()[start + n];
}
StringPiece KeyedSparseTensorColumn<StringPiece>::Feature(
    int64 batch, int64 n, bool strong_hash) const {
  const int64 start = feature_start_indices_[batch];
  return values_.vec<tstring>().data()[start + n];
}