pitrou commented on a change in pull request #10606:
URL: https://github.com/apache/arrow/pull/10606#discussion_r663466643
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File path: cpp/src/arrow/compute/kernels/vector_selection.cc
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@@ -1668,6 +1668,66 @@ struct ListImpl : public Selection<ListImpl<Type>, Type>
{
}
};
+struct DenseUnionImpl : public Selection<DenseUnionImpl, DenseUnionType> {
+ using Base = Selection<DenseUnionImpl, DenseUnionType>;
+ LIFT_BASE_MEMBERS();
+
+ typename TypeTraits<DenseUnionType>::ValueOffsetBuilderType
value_offset_builder;
+ typename TypeTraits<DenseUnionType>::ChildIdBuilderType child_id_builder;
+ std::vector<int8_t> type_codes;
+
+ DenseUnionImpl(KernelContext* ctx, const ExecBatch& batch, int64_t
output_length,
+ Datum* out)
+ : Base(ctx, batch, output_length, out),
+ value_offset_builder(ctx->memory_pool()),
+ child_id_builder(ctx->memory_pool()) {
+ DenseUnionArray typed_values(this->values);
+ type_codes = typed_values.union_type()->type_codes();
+ }
+
+ template <typename Adapter>
+ Status GenerateOutput() {
+ DenseUnionArray typed_values(this->values);
+ Adapter adapter(this);
+ RETURN_NOT_OK(adapter.Generate(
+ [&](int64_t index) {
+ auto child_id = typed_values.child_id(index);
+ child_id_builder.UnsafeAppend(type_codes[child_id]);
+ auto value_offset = typed_values.value_offset(index);
+ value_offset_builder.UnsafeAppend(value_offset);
+ return Status::OK();
+ },
+ // TODO: not able to handle null case
+ VisitNoop));
+ return Status::OK();
+ }
+
+ Status Init() override {
+ RETURN_NOT_OK(child_id_builder.Reserve(output_length));
+ RETURN_NOT_OK(value_offset_builder.Reserve(output_length));
+ return Status::OK();
+ }
+
+ Status Finish() override {
+ std::shared_ptr<Array> child_ids;
+ std::shared_ptr<Array> value_offsets;
+ RETURN_NOT_OK(child_id_builder.Finish(&child_ids));
+ RETURN_NOT_OK(value_offset_builder.Finish(&value_offsets));
+
+ DenseUnionArray typed_values(this->values);
+ auto num_fields = typed_values.num_fields();
+ ArrayVector child_arrays;
+ child_arrays.reserve(num_fields);
+ BufferVector buffers = {nullptr, checked_cast<const
Int8Array&>(*child_ids).values(),
+ checked_cast<const
Int32Array&>(*value_offsets).values()};
+ *out = ArrayData(typed_values.type(), child_ids->length(),
std::move(buffers), 0);
+ for (int i = 0; i < typed_values.num_fields(); i++) {
+ out->child_data.push_back(typed_values.field(i)->data());
Review comment:
I don't think you need to use any child builders. Instead, you should be
able to call `Take` on each of the child arrays; you just have to construct the
indices carefully for each child array.
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