Neater implementation

Tom-Newton · Jan 14, 2025 · 7a3a569 · 7a3a569
1 parent 44ac772
commit 7a3a569
Showing 1 changed file with 4 additions and 26 deletions.
diff --git a/cpp/src/arrow/compute/kernels/scalar_cast_nested.cc b/cpp/src/arrow/compute/kernels/scalar_cast_nested.cc
@@ -17,7 +17,6 @@
 
 // Implementation of casting to (or between) list types
 
-#include <iostream>
 #include <limits>
 #include <map>
 #include <utility>
@@ -342,12 +341,6 @@ struct CastFixedList {
 
 struct CastStruct {
   static Status Exec(KernelContext* ctx, const ExecSpan& batch, ExecResult* out) {
-    // The equivalent logic for top level columns is
-    // https://github.com/apache/arrow/blob/6252e9ceeb0f8544c14f79d895a37ac198131f88/cpp/src/arrow/compute/expression.cc#L669
-    // - For top level columns duplicate names are considered an error when reading
-    // - When casting tables, reordering or filling top level columns with null is not
-    //   supported. These behaviours are implemented in MakeExecBatch which seems to be
-    //   used for scanning datasets and constructing data from expressions.
     static constexpr int kFillNullSentinel = -2;
 
     const CastOptions& options = CastState::Get(ctx);
@@ -365,29 +358,14 @@ struct CastStruct {
 
     for (int out_field_index = 0; out_field_index < out_field_count; ++out_field_index) {
       const auto& out_field = out_type.field(out_field_index);
-      auto maybe_in_field_indexes = in_fields.equal_range(out_field->name());
-      // for (const auto& field : in_fields) {
-      //   std::cout << "Field name: " << field.first << ", Field index: " << field.second
-      //             << std::endl;
-      // }
-      // std::cout << std::endl;
-      if (maybe_in_field_indexes.first != maybe_in_field_indexes.second) {
-        // There is at least one in_field with matching name.
-        const auto& in_field_index = maybe_in_field_indexes.first->second;
-        const auto& in_field = in_type.field(maybe_in_field_indexes.first->second);
+      auto maybe_in_field_index = in_fields.extract(out_field->name());
+      if (!maybe_in_field_index.empty()) {
+        const auto& in_field = in_type.field(maybe_in_field_index.mapped());
         if (in_field->nullable() && !out_field->nullable()) {
           return Status::TypeError("cannot cast nullable field to non-nullable field: ",
                                    in_type.ToString(), " ", out_type.ToString());
         }
-
-        in_fields.erase(maybe_in_field_indexes.first);
-        // if (maybe_in_field_indexes.first != --maybe_in_field_indexes.second) {
-        //   // There is more than one `in_field` with matching name. Remove the one we
-        //   are
-        //   // using to maintain column order in the case that the output struct also has
-        //   // duplicate field names.
-        // }
-        fields_to_select[out_field_index] = in_field_index;
+        fields_to_select[out_field_index] = maybe_in_field_index.mapped();
       } else if (out_field->nullable()) {
         fields_to_select[out_field_index] = kFillNullSentinel;
       } else {