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From "Kai Sasaki (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (SPARK-8419) Statistics.colStats could avoid an extra count()
Date Sun, 21 Jun 2015 13:48:00 GMT

    [ https://issues.apache.org/jira/browse/SPARK-8419?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14595048#comment-14595048
] 

Kai Sasaki commented on SPARK-8419:
-----------------------------------

In the {{Statistics#colStats}}, the number of rows seems to be updated in {{computeColumnSummaryStatistics}}
with {{updateNumRows}}. This is computed through distributed process which is calculated inside
of {{RDD#treeAggregate}}. So I think there is no extra {{count()}} when just only creating
{{RowMatrix}}. Is this assumption correct?

> Statistics.colStats could avoid an extra count()
> ------------------------------------------------
>
>                 Key: SPARK-8419
>                 URL: https://issues.apache.org/jira/browse/SPARK-8419
>             Project: Spark
>          Issue Type: Improvement
>          Components: MLlib
>            Reporter: Joseph K. Bradley
>            Priority: Trivial
>              Labels: starter
>
> Statistics.colStats goes through RowMatrix to compute the stats.  But RowMatrix.computeColumnSummaryStatistics
does an extra count() which could be avoided.  Not going through RowMatrix would skip this
extra pass over the data.



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