kou commented on code in PR #39362:
URL: https://github.com/apache/arrow/pull/39362#discussion_r1442156182
##########
cpp/src/arrow/compute/kernels/scalar_cast_dictionary.cc:
##########
@@ -77,17 +85,23 @@ Status CastToDictionary(KernelContext* ctx, const ExecSpan&
batch, ExecResult* o
return Status::OK();
}
-std::vector<std::shared_ptr<CastFunction>> GetDictionaryCasts() {
- auto func = std::make_shared<CastFunction>("cast_dictionary",
Type::DICTIONARY);
-
- AddCommonCasts(Type::DICTIONARY, kOutputTargetType, func.get());
- ScalarKernel kernel({InputType(Type::DICTIONARY)}, kOutputTargetType,
CastToDictionary);
+template <typename SrcType>
+void AddDictionaryCast(CastFunction* func) {
+ ScalarKernel kernel;
+ kernel.exec = CastToDictionary;
+ kernel.signature =
+ KernelSignature::Make({InputType(SrcType::type_id)}, kOutputTargetType);
kernel.null_handling = NullHandling::COMPUTED_NO_PREALLOCATE;
- kernel.mem_allocation = MemAllocation::NO_PREALLOCATE;
Review Comment:
Can we keep this for `DictionaryType`?
##########
cpp/src/arrow/scalar_test.cc:
##########
@@ -1479,11 +1479,12 @@ TEST(TestDictionaryScalar, Cast) {
auto alpha =
dict->IsValid(i) ? MakeScalar(dict->GetString(i)) :
MakeNullScalar(utf8());
// Cast string to dict(..., string)
- ASSERT_OK_AND_ASSIGN(auto cast_alpha, alpha->CastTo(ty));
- ASSERT_OK(cast_alpha->ValidateFull());
+ ASSERT_OK_AND_ASSIGN(auto cast_alpha, Cast(alpha, ty));
+ const auto& scalar = cast_alpha.scalar();
Review Comment:
How about keeping `cast_alpha` name? It's more meaningful than `scalar`.
```suggestion
ASSERT_OK_AND_ASSIGN(auto cast_alpha_datum, Cast(alpha, ty));
const auto& cast_alpha = cast_alpha_datum.scalar();
```
##########
cpp/src/arrow/compute/kernels/scalar_cast_dictionary.cc:
##########
@@ -44,6 +44,14 @@ Status CastToDictionary(KernelContext* ctx, const ExecSpan&
batch, ExecResult* o
}
std::shared_ptr<ArrayData> in_array = batch[0].array.ToArrayData();
+
+ // If the input type is STRING, it is first encoded as a dictionary to
facilitate
+ // processing. This approach allows the subsequent code to uniformly handle
STRING
+ // inputs as if they were originally provided in dictionary format. Encoding
as a
+ // dictionary helps in reusing the same logic for dictionary operations.
+ if (batch[0].type()->id() == Type::STRING) {
+ in_array = DictionaryEncode(batch[0].array.ToArrayData())->array();
Review Comment:
Can we use `in_array` here?
```suggestion
in_array = DictionaryEncode(in_array)->array();
```
##########
cpp/src/arrow/compute/kernels/scalar_cast_dictionary.cc:
##########
@@ -77,17 +85,23 @@ Status CastToDictionary(KernelContext* ctx, const ExecSpan&
batch, ExecResult* o
return Status::OK();
}
-std::vector<std::shared_ptr<CastFunction>> GetDictionaryCasts() {
- auto func = std::make_shared<CastFunction>("cast_dictionary",
Type::DICTIONARY);
-
- AddCommonCasts(Type::DICTIONARY, kOutputTargetType, func.get());
- ScalarKernel kernel({InputType(Type::DICTIONARY)}, kOutputTargetType,
CastToDictionary);
+template <typename SrcType>
+void AddDictionaryCast(CastFunction* func) {
+ ScalarKernel kernel;
+ kernel.exec = CastToDictionary;
+ kernel.signature =
+ KernelSignature::Make({InputType(SrcType::type_id)}, kOutputTargetType);
kernel.null_handling = NullHandling::COMPUTED_NO_PREALLOCATE;
- kernel.mem_allocation = MemAllocation::NO_PREALLOCATE;
+ DCHECK_OK(func->AddKernel(SrcType::type_id, std::move(kernel)));
+}
- DCHECK_OK(func->AddKernel(Type::DICTIONARY, std::move(kernel)));
+std::vector<std::shared_ptr<CastFunction>> GetDictionaryCasts() {
+ auto cast_dict = std::make_shared<CastFunction>("cast_dictionary",
Type::DICTIONARY);
+ AddCommonCasts(Type::DICTIONARY, kOutputTargetType, cast_dict.get());
+ AddDictionaryCast<DictionaryType>(cast_dict.get());
+ AddDictionaryCast<StringType>(cast_dict.get());
Review Comment:
Can we use `arrow::StringTypes()` for all string types (`StringType` and
`LargeStringType`)?
(We may want to add support for `BinaryType` and `LargeBinaryType` as a
separated PR.)
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