wjones127 commented on code in PR #14198:
URL: https://github.com/apache/arrow/pull/14198#discussion_r982812957
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cpp/src/arrow/compute/kernels/scalar_cast_nested.cc:
##########
@@ -206,6 +211,75 @@ void AddStructToStructCast(CastFunction* func) {
DCHECK_OK(func->AddKernel(StructType::type_id, std::move(kernel)));
}
+template <typename DestType>
+struct CastMap {
+ using CastListImpl = CastList<MapType, DestType>;
+
+ static Status Exec(KernelContext* ctx, const ExecSpan& batch, ExecResult*
out) {
+ const CastOptions& options = CastState::Get(ctx);
+
+ std::shared_ptr<DataType> entry_type =
+ checked_cast<const DestType&>(*out->type()).value_type();
+ // Assert is struct with two fields
+ if (!(entry_type->id() == Type::STRUCT && entry_type->num_fields() == 2)) {
+ return Status::TypeError(
+ "Map type must be cast to a list<struct> with exactly two fields.");
+ }
+ std::shared_ptr<DataType> key_type = entry_type->field(0)->type();
+ std::shared_ptr<DataType> value_type = entry_type->field(1)->type();
+
+ const ArraySpan& in_array = batch[0].array;
+
+ ArrayData* out_array = out->array_data().get();
+ out_array->buffers[0] = in_array.GetBuffer(0);
+ out_array->buffers[1] = in_array.GetBuffer(1);
+
+ std::shared_ptr<ArrayData> entries = in_array.child_data[0].ToArrayData();
+
+ RETURN_NOT_OK(CastListImpl::HandleOffsets(ctx, in_array, out_array,
&entries));
+
+ // Handle keys
+ const std::shared_ptr<ArrayData>& keys =
+ entries->child_data[0]->Slice(entries->offset, entries->length);
+ ARROW_ASSIGN_OR_RAISE(Datum cast_keys,
+ Cast(keys, key_type, options, ctx->exec_context()));
+ DCHECK(cast_keys.is_array());
+
+ // Handle values
+ const std::shared_ptr<ArrayData>& values =
+ entries->child_data[1]->Slice(entries->offset, entries->length);
+ ARROW_ASSIGN_OR_RAISE(Datum cast_values,
+ Cast(values, value_type, options,
ctx->exec_context()));
+ DCHECK(cast_values.is_array());
+
+ // Copy null bitmap
+ std::shared_ptr<Buffer> null_bitmap;
+ if (in_array.buffers[0].data != nullptr) {
Review Comment:
Whoops this part is dead code. I had the validity bitmap handling in
`HandleOffsets()`, but that's a little confusing, so I'll put it out of there.
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