[GitHub] spark pull request: [SPARK-9298][SQL] Add pearson correlation aggr...

[mengxr <gi...@git.apache.org>]

Github user mengxr commented on the pull request:

    https://github.com/apache/spark/pull/8587#issuecomment-149650308
  
    @viirya We compared the performance of declarative approach vs imperative in https://issues.apache.org/jira/browse/SPARK-10953. The declarative approach is much slower because of extra code and lack of common sub-expression elimination. If you still keep the original code, could you revert this PR to your first commit? Also cc @rxin for this performance issue.


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