Function ListFromListViewImpl

cpp/src/arrow/array/array_nested.cc:410–447

template <typename DestListType, typename SrcListViewType>
Result<std::shared_ptr<ArrayData>> ListFromListViewImpl(
    const std::shared_ptr<ArrayData>& list_view_data, MemoryPool* pool) {
  static_assert(
      std::is_same<typename SrcListViewType::offset_type,
                   typename DestListType::offset_type>::value,
      "Offset types between list type and list-view type are expected to match");
  using offset_type = typename DestListType::offset_type;
  using ListBuilderType = typename TypeTraits<DestListType>::BuilderType;

  const auto& list_view_type =
      checked_cast<const SrcListViewType&>(*list_view_data->type);
  const auto& value_type = list_view_type.value_type();
  const auto list_type = std::make_shared<DestListType>(value_type);

  ARROW_ASSIGN_OR_RAISE(auto sum_of_list_view_sizes,
                        list_util::internal::SumOfLogicalListSizes(*list_view_data));
  ARROW_ASSIGN_OR_RAISE(std::shared_ptr<ArrayBuilder> value_builder,
                        MakeBuilder(value_type, pool));
  RETURN_NOT_OK(value_builder->Reserve(sum_of_list_view_sizes));
  auto list_builder = std::make_shared<ListBuilderType>(pool, value_builder, list_type);
  RETURN_NOT_OK(list_builder->Reserve(list_view_data->length));

  ArraySpan values{*list_view_data->child_data[0]};
  const auto* in_validity_bitmap = list_view_data->GetValues<uint8_t>(0);
  const auto* in_offsets = list_view_data->GetValues<offset_type>(1);
  const auto* in_sizes = list_view_data->GetValues<offset_type>(2);
  for (int64_t i = 0; i < list_view_data->length; ++i) {
    const bool is_valid =
        !in_validity_bitmap ||
        bit_util::GetBit(in_validity_bitmap, list_view_data->offset + i);
    const int64_t size = is_valid ? in_sizes[i] : 0;
    RETURN_NOT_OK(list_builder->Append(is_valid, size));
    RETURN_NOT_OK(value_builder->AppendArraySlice(values, in_offsets[i], size));
  }
  std::shared_ptr<ArrayData> list_array_data;
  RETURN_NOT_OK(list_builder->FinishInternal(&list_array_data));
  return list_array_data;
}

}  // namespace