wjones127 commented on code in PR #37292:
URL: https://github.com/apache/arrow/pull/37292#discussion_r1301779157
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cpp/src/arrow/compute/kernels/scalar_cast_nested.cc:
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@@ -145,6 +153,135 @@ void AddListCast(CastFunction* func) {
DCHECK_OK(func->AddKernel(SrcType::type_id, std::move(kernel)));
}
+template <typename DestType>
+struct CastFixedToVarList {
+ using dest_offset_type = typename DestType::offset_type;
+
+ static Status Exec(KernelContext* ctx, const ExecSpan& batch, ExecResult*
out) {
+ const CastOptions& options = CastState::Get(ctx);
+
+ auto child_type = checked_cast<const DestType&>(*out->type()).value_type();
+
+ const ArraySpan& in_array = batch[0].array;
+
+ ArrayData* out_array = out->array_data().get();
+ ARROW_ASSIGN_OR_RAISE(out_array->buffers[0],
+ GetNullBitmapBuffer(in_array, ctx->memory_pool()));
+
+ const auto& in_type = checked_cast<const
FixedSizeListType&>(*in_array.type);
+ const int32_t list_size = in_type.list_size();
+
+ // Allocate a new offsets buffer
+ ARROW_ASSIGN_OR_RAISE(out_array->buffers[1],
+ ctx->Allocate(sizeof(dest_offset_type) *
(batch.length + 1)));
+ auto* offsets = out_array->GetMutableValues<dest_offset_type>(1);
+ dest_offset_type offset = 0;
+ for (int64_t i = 0; i <= batch.length; ++i) {
+ offsets[i] = offset;
+ offset += list_size;
+ }
+
+ // Handle values
+ std::shared_ptr<ArrayData> values = in_array.child_data[0].ToArrayData();
+ if (in_array.offset > 0 || (in_array.length * list_size < batch.length)) {
Review Comment:
Actually, I think the second condition might be unnecessary. The offsets
will already determine the end of the array, so we shouldn't need to slice the
values if there isn't an offset.
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