[GitHub] [arrow] nealrichardson commented on a change in pull request #7435: ARROW-8779: [R] Implement conversion to List

[GitBox <gi...@apache.org>]

nealrichardson commented on a change in pull request #7435:
URL: https://github.com/apache/arrow/pull/7435#discussion_r443735874



##########
File path: r/src/array_from_vector.cpp
##########
@@ -201,6 +202,67 @@ struct VectorToArrayConverter {
     return Status::OK();
   }
 
+  template <typename T>
+  arrow::enable_if_t<is_struct_type<T>::value, Status> Visit(const T& type) {
+    using BuilderType = typename TypeTraits<T>::BuilderType;
+    ARROW_RETURN_IF(!Rf_inherits(x, "data.frame"),
+                    Status::RError("Expecting a data frame"));
+
+    auto* struct_builder = checked_cast<BuilderType*>(builder);
+
+    int64_t n = vctrs::short_vec_size(x);

Review comment:
       See also https://jira.apache.org/jira/browse/ARROW-9028 and some skipped tests about tables with 0 columns




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