lidavidm commented on a change in pull request #12724:
URL: https://github.com/apache/arrow/pull/12724#discussion_r836377718
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File path: cpp/src/arrow/compute/kernels/scalar_cast_nested.cc
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@@ -228,6 +228,107 @@ void AddStructToStructCast(CastFunction* func) {
DCHECK_OK(func->AddKernel(StructType::type_id, std::move(kernel)));
}
+struct CastStructSubset {
+ static Status Exec(KernelContext* ctx, const ExecBatch& batch, Datum* out) {
+ const CastOptions& options = CastState::Get(ctx);
+ const auto& in_type = checked_cast<const StructType&>(*batch[0].type());
+ const auto& out_type = checked_cast<const StructType&>(*out->type());
+ const int in_field_count = in_type.num_fields();
+ const int out_field_count = out_type.num_fields();
+
+ std::vector<bool> fields_to_select(in_field_count, false);
+
+ int out_field_index = 0;
+ for (int in_field_index = 0;
+ in_field_index < in_field_count && out_field_index < out_field_count;
+ ++in_field_index) {
+ const auto in_field = in_type.field(in_field_index);
+ const auto out_field = out_type.field(out_field_index);
+ if (in_field->name() == out_field->name()) {
+ if (in_field->nullable() && !out_field->nullable()) {
+ return Status::TypeError("cannot cast nullable struct to
non-nullable struct: ",
+ in_type.ToString(), " ",
out_type.ToString());
+ }
+ fields_to_select[in_field_index] = true;
+ ++out_field_index;
+ }
+ }
+
+ if (out_field_index < out_field_count - 1) {
+ return Status::TypeError(
+ "struct subfields names don't match or are in the wrong order: ",
+ in_type.ToString(), " ", out_type.ToString());
+ }
+
+ if (out->kind() == Datum::SCALAR) {
+ const auto& in_scalar = checked_cast<const
StructScalar&>(*batch[0].scalar());
+ auto out_scalar = checked_cast<StructScalar*>(out->scalar().get());
+
+ DCHECK(!out_scalar->is_valid);
+ if (in_scalar.is_valid) {
+ out_field_index = 0;
+ for (int in_field_index = 0; in_field_index < in_field_count;
in_field_index++) {
+ if (fields_to_select[in_field_index]) {
+ auto values = in_scalar.value[in_field_index];
+ auto target_type = out->type()->field(out_field_index++)->type();
+ ARROW_ASSIGN_OR_RAISE(Datum cast_values, Cast(values, target_type,
options,
+
ctx->exec_context()));
+ DCHECK_EQ(Datum::SCALAR, cast_values.kind());
+ out_scalar->value.push_back(cast_values.scalar());
+ }
+ }
+ out_scalar->is_valid = true;
+ }
+ return Status::OK();
+ }
+
+ const ArrayData& in_array = *batch[0].array();
+ ArrayData* out_array = out->mutable_array();
+
+ if (in_array.GetNullCount() > 0) {
+ auto out_bitmap_builder = TypedBufferBuilder<bool>(ctx->memory_pool());
+ const auto in_bitmap = in_array.buffers[0]->data();
+
+ for (int in_field_index = 0; in_field_index < in_field_count;
in_field_index++) {
+ if (fields_to_select[in_field_index]) {
+ if (bit_util::GetBit(in_bitmap, in_array.offset + in_field_index)) {
+ ARROW_RETURN_NOT_OK(out_bitmap_builder.Append(true));
+ } else {
+ ARROW_RETURN_NOT_OK(out_bitmap_builder.Append(false));
+ }
+ }
+ }
+ ARROW_ASSIGN_OR_RAISE(out_array->buffers[0],
out_bitmap_builder.Finish());
+ }
+
+ out_field_index = 0;
+ for (int in_field_index = 0; in_field_index < in_field_count;
in_field_index++) {
+ if (fields_to_select[in_field_index]) {
+ auto values =
+ in_array.child_data[in_field_index]->Slice(in_array.offset,
in_array.length);
+ auto target_type = out->type()->field(out_field_index++)->type();
+
+ ARROW_ASSIGN_OR_RAISE(Datum cast_values,
+ Cast(values, target_type, options,
ctx->exec_context()));
+
+ DCHECK_EQ(Datum::ARRAY, cast_values.kind());
+ out_array->child_data.push_back(cast_values.array());
+ }
+ }
+
+ return Status::OK();
+ }
+};
+
+void AddStructToStructSubsetCast(CastFunction* func) {
+ ScalarKernel kernel;
+ kernel.exec = CastStructSubset::Exec;
+ kernel.signature =
+ KernelSignature::Make({InputType(StructType::type_id)},
kOutputTargetType);
+ kernel.null_handling = NullHandling::COMPUTED_NO_PREALLOCATE;
+ DCHECK_OK(func->AddKernel(StructType::type_id, std::move(kernel)));
+}
Review comment:
Why can't we implement it as part of the existing cast instead of having
a separate one?
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