fsaintjacques commented on a change in pull request #7026:
URL: https://github.com/apache/arrow/pull/7026#discussion_r417218364
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File path: cpp/src/arrow/scalar.cc
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@@ -252,6 +270,100 @@ Result<std::shared_ptr<Scalar>> Scalar::Parse(const
std::shared_ptr<DataType>& t
return ScalarParseImpl{type, s}.Finish();
}
+struct ScalarFromArraySlotImpl {
+ template <typename T>
+ using ScalarType = typename TypeTraits<T>::ScalarType;
+
+ Status Visit(const NullArray& a) {
+ out_ = std::make_shared<NullScalar>();
+ return Status::OK();
+ }
+
+ Status Visit(const BooleanArray& a) { return Finish(a.Value(index_)); }
+
+ template <typename T>
+ Status Visit(const NumericArray<T>& a) {
+ return Finish(a.Value(index_));
+ }
+
+ template <typename T>
+ Status Visit(const BaseBinaryArray<T>& a) {
+ return Finish(a.GetString(index_));
+ }
+
+ Status Visit(const FixedSizeBinaryArray& a) { return
Finish(a.GetString(index_)); }
+
+ Status Visit(const DayTimeIntervalArray& a) { return
Finish(a.Value(index_)); }
+
+ template <typename T>
+ Status Visit(const BaseListArray<T>& a) {
+ return Finish(a.value_slice(index_));
+ }
+
+ Status Visit(const FixedSizeListArray& a) { return
Finish(a.value_slice(index_)); }
+
+ Status Visit(const StructArray& a) {
+ ScalarVector children;
+ for (const auto& child : a.fields()) {
+ children.emplace_back();
+ ARROW_ASSIGN_OR_RAISE(children.back(), Scalar::FromArraySlot(*child,
index_));
+ }
+ return Finish(std::move(children));
+ }
+
+ Status Visit(const UnionArray& a) {
+ return Status::NotImplemented("Non-null UnionScalar");
+ }
+
+ Status Visit(const DictionaryArray& a) {
+ ARROW_ASSIGN_OR_RAISE(auto index, Scalar::FromArraySlot(*a.indices(),
index_));
Review comment:
Multiple problems here:
1. Confusing naming with `index`, `index_`, `index64`,
2. We shouldn't use Scalar because its dynamic typing is convenient,, it
should stick to C++ type system. You can add a method `int64_t
DictionaryArray::GetValueIndex(int64_t row_index)` that will properly upcast to
int64_t independent of `indices` type. This Visit method becomes trivial
afterward.
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