[jira] [Commented] (SPARK-14408) Update RDD.treeAggregate not to use reduce

["Apache Spark (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/SPARK-14408?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16036516#comment-16036516 ] 

Apache Spark commented on SPARK-14408:
--------------------------------------

User 'HyukjinKwon' has created a pull request for this issue:
https://github.com/apache/spark/pull/18198

> Update RDD.treeAggregate not to use reduce
> ------------------------------------------
>
>                 Key: SPARK-14408
>                 URL: https://issues.apache.org/jira/browse/SPARK-14408
>             Project: Spark
>          Issue Type: Bug
>          Components: ML, MLlib, Spark Core
>            Reporter: Joseph K. Bradley
>            Assignee: Joseph K. Bradley
>            Priority: Minor
>
> **Issue**
> In MLlib, we have assumed that {{RDD.treeAggregate}} allows the {{seqOp}} and {{combOp}} functions to modify and return their first argument, just like {{RDD.aggregate}}.  However, it is not documented that way.
> I started to add docs to this effect, but then noticed that {{treeAggregate}} uses {{reduceByKey}} and {{reduce}} in its implementation, neither of which technically allows the seq/combOps to modify and return their first arguments.
> **Question**: Is the implementation safe, or does it need to be updated?
> **Decision**: Avoid using reduce.  Use fold instead.



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