[C++] Change parquet::arrow::FileReader::ReadRowGroups to read into contiguous arrays

[asfimport]

Instead of creating a chunk per RowGroup, we should read at least for primitive type into a single, pre-allocated Array. This needs some new functionality in the Record reader classes and thus should be done after apache/parquet-cpp#462 is merged.

Reporter: Uwe Korn / @xhochy
Assignee: Wes McKinney / @wesm

Related issues:

• [C++] Basic RowGroup filtering (relates to)

_{Note: This issue was originally created as ARROW-3774. Please see the migration documentation for further details.}

[asfimport]

Wes McKinney / @wesm:
I'm not sure this is really useful. Closing

[asfimport]

Wes McKinney / @wesm:
The main use case would be for pandas (where things need to be contiguous), but there memory will have to be copied in general when calling pyarrow.Table.to_pandas, so the benefits of this optimization would be minimal, if any. Producing large contiguous arrays could even be more expensive than the current behavior of creating chunked arrays