[GitHub] [arrow] emkornfield commented on pull request #7704: ARROW-9297: [C++][Parquet] Support chunked row groups in RowGroupRecordBatchReader

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

emkornfield commented on pull request #7704:
URL: https://github.com/apache/arrow/pull/7704#issuecomment-657119271


   I prefer checks to assertions for 'in the wild' errors.  Especially around
   code that is acting on passed data.
   
   On Saturday, July 11, 2020, Benjamin Kietzman <no...@github.com>
   wrote:
   
   > *@bkietz* commented on this pull request.
   > ------------------------------
   >
   > In cpp/src/parquet/arrow/schema.h
   > <https://github.com/apache/arrow/pull/7704#discussion_r453228008>:
   >
   > >      // Coalesce a list of schema field indices which are the roots of the
   >      // columns referred to by a list of column indices
   >      const schema::GroupNode* group = descr->group_node();
   >      std::unordered_set<int> already_added;
   > -    out->clear();
   > -    for (auto& column_idx : column_indices) {
   > +
   > +    std::vector<int> out;
   > +    for (int column_idx : column_indices) {
   > +      if (column_idx < 0 || column_idx >= descr->num_columns()) {
   > +        return ::arrow::Status::IndexError("Column index ", column_idx, " is not valid");
   > +      }
   >        auto field_node = descr->GetColumnRoot(column_idx);
   >        auto field_idx = group->FieldIndex(*field_node);
   >        if (field_idx < 0) {
   >
   > Worth noting: replacing this check with an assertion locally broke no
   > tests in C++ or python. I'll leave it as an assertion for now and see what
   > CI thinks
   >
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