Function MakeListArray

cpp/src/parquet/arrow/test_util.h:382–417

Wrap an Array into a ListArray by splitting it up into size lists. This helper function only supports (size/2) nulls.

///
/// This helper function only supports (size/2) nulls.
Status MakeListArray(const std::shared_ptr<Array>& values, int64_t size,
                     int64_t null_count, const std::string& item_name,
                     bool nullable_values, std::shared_ptr<::arrow::ListArray>* out) {
  // We always include an empty list
  int64_t non_null_entries = size - null_count - 1;
  int64_t length_per_entry = values->length() / non_null_entries;

  auto offsets = AllocateBuffer();
  RETURN_NOT_OK(offsets->Resize((size + 1) * sizeof(int32_t)));
  int32_t* offsets_ptr = reinterpret_cast<int32_t*>(offsets->mutable_data());

  auto null_bitmap = AllocateBuffer();
  int64_t bitmap_size = ::arrow::bit_util::BytesForBits(size);
  RETURN_NOT_OK(null_bitmap->Resize(bitmap_size));
  uint8_t* null_bitmap_ptr = null_bitmap->mutable_data();
  memset(null_bitmap_ptr, 0, bitmap_size);

  int32_t current_offset = 0;
  for (int64_t i = 0; i < size; i++) {
    offsets_ptr[i] = current_offset;
    if (!(((i % 2) == 0) && ((i / 2) < null_count))) {
      // Non-null list (list with index 1 is always empty).
      ::arrow::bit_util::SetBit(null_bitmap_ptr, i);
      if (i != 1) {
        current_offset += static_cast<int32_t>(length_per_entry);
      }
    }
  }
  offsets_ptr[size] = static_cast<int32_t>(values->length());

  auto value_field = ::arrow::field(item_name, values->type(), nullable_values);
  *out = std::make_shared<::arrow::ListArray>(::arrow::list(value_field), size, offsets,
                                              values, null_bitmap, null_count);

  return Status::OK();
}

// Make an array containing only empty lists, with a null values array
Status MakeEmptyListsArray(int64_t size, std::shared_ptr<Array>* out_array) {