lidavidm commented on a change in pull request #12248:
URL: https://github.com/apache/arrow/pull/12248#discussion_r803250810
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File path: cpp/src/arrow/compute/kernels/scalar_cast_nested.cc
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@@ -150,6 +150,104 @@ void AddListCast(CastFunction* func) {
DCHECK_OK(func->AddKernel(SrcType::type_id, std::move(kernel)));
}
+struct CastStruct {
+ static Status Exec(KernelContext* ctx, const ExecBatch& batch, Datum* out) {
+ const CastOptions& options = CastState::Get(ctx);
+ const auto in_field_count =
+ checked_cast<const StructType&>(*batch[0].type()).num_fields();
+ const auto out_field_count =
+ checked_cast<const StructType&>(*out->type()).num_fields();
+
+ if (in_field_count != out_field_count) {
+ return Status::TypeError("struct field sizes do not match: ",
+ batch[0].type()->ToString(), " ",
out->type()->ToString());
+ }
+
+ for (int i = 0; i < in_field_count; ++i) {
+ const auto in_field_name =
+ checked_cast<const StructType&>(*batch[0].type()).field(i)->name();
+ const auto out_field_name =
+ checked_cast<const StructType&>(*out->type()).field(i)->name();
+ if (in_field_name != out_field_name) {
+ return Status::TypeError(
+ "struct field names do not match: ", batch[0].type()->ToString(),
" ",
+ out->type()->ToString());
+ }
+
+ const auto in_field_nullable =
+ checked_cast<const
StructType&>(*batch[0].type()).field(i)->nullable();
+ const auto out_field_nullable =
+ checked_cast<const StructType&>(*out->type()).field(i)->nullable();
+
+ if (in_field_nullable && !out_field_nullable) {
+ return Status::TypeError("cannot cast nullable struct to non-nullable
struct: ",
+ batch[0].type()->ToString(), " ",
+ out->type()->ToString());
+ }
+ }
+
+ for (int i = 0; i < in_field_count; ++i) {
+ const auto in_field_name =
+ checked_cast<const StructType&>(*batch[0].type()).field(i)->name();
+ const auto out_field_name =
+ checked_cast<const StructType&>(*out->type()).field(i)->name();
+ if (in_field_name != out_field_name) {
+ return Status::TypeError(
+ "struct field names do not match: ", batch[0].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) {
+ for (int i = 0; i < in_field_count; i++) {
+ auto values = in_scalar.value[i];
+ auto target_type = out->type()->field(i)->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();
+ out_array->buffers = in_array.buffers;
Review comment:
Sorry, there's lots of knobs to turn for this, so there's not one
obvious way to implement things. I would see if `kernel.null_handling` +
slicing children before casting works (it should, as far as I can tell without
building and trying it myself.)
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