Function DetectSparseCOOIndexCanonicality

cpp/src/arrow/sparse_tensor.cc:183–215

}

bool DetectSparseCOOIndexCanonicality(const std::shared_ptr<Tensor>& coords) {
  DCHECK_EQ(coords->ndim(), 2);

  const auto& shape = coords->shape();
  const int64_t non_zero_length = shape[0];
  if (non_zero_length <= 1) return true;

  const int64_t ndim = shape[1];
  std::vector<int64_t> last_index, index;
  GetCOOIndexTensorRow(coords, 0, &last_index);
  for (int64_t i = 1; i < non_zero_length; ++i) {
    GetCOOIndexTensorRow(coords, i, &index);
    int64_t j = 0;
    while (j < ndim) {
      if (last_index[j] > index[j]) {
        // last_index > index, so we can detect non-canonical here
        return false;
      }
      if (last_index[j] < index[j]) {
        // last_index < index, so we can skip the remaining dimensions
        break;
      }
      ++j;
    }
    if (j == ndim) {
      // last_index == index, so we can detect non-canonical here
      return false;
    }
    swap(last_index, index);
  }

  return true;
}

}  // namespace