[GitHub] [arrow] westonpace commented on a change in pull request #8984: ARROW-5336: [C++] Implement arrow::Concatenate for dictionary-encoded arrays with unequal dictionaries

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westonpace commented on a change in pull request #8984:
URL: https://github.com/apache/arrow/pull/8984#discussion_r546934934



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File path: cpp/src/arrow/array/array_dict.cc
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@@ -44,6 +44,29 @@ namespace arrow {
 using internal::checked_cast;
 using internal::CopyBitmap;
 
+struct MaxIndexAccessor {

Review comment:
       The DictionaryUnifier is typed to the value type of the dictionary but not the index type so I needed to create this utility for accessing the max possible value for a given index type.  I wasn't really sure where to put this.  There could also be a general purpose visitor for finding the min/max of all numeric types.  Also, do we have this capability anywhere else in the code base I could just leverage?  This is needed by DictionaryUnifierImpl::GetResultWithIndexType




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