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https://issues.apache.org/jira/browse/DRILL-4566?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15218852#comment-15218852
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ASF GitHub Bot commented on DRILL-4566:
---------------------------------------

GitHub user StevenMPhillips opened a pull request:

    https://github.com/apache/drill/pull/456

    DRILL-4566: TDigest, median, and quantile functions

    Adds tdigest, tdigest_merge, median, and quantile UDFS
    Adds reduce aggregates rule to reduce:
      median(x) -> tdigest_median(tdigest(x))
      quantile(q, x) -> tdigest_quantile(q, tdigest(x))
    Adds two-phase aggregate rule for tdigest
    
    Also adds ability to specify tolerances in the TestBuilder

You can merge this pull request into a Git repository by running:

    $ git pull https://github.com/StevenMPhillips/drill drill-4566

Alternatively you can review and apply these changes as the patch at:

    https://github.com/apache/drill/pull/456.patch

To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:

    This closes #456
    
----
commit b6a90053c7451d92b15807ba50057f5790985efc
Author: Steven Phillips <ste...@dremio.com>
Date:   2016-03-30T01:55:26Z

    DRILL-4566: TDigest, median, and quantile functions
    
    Adds tdigest, tdigest_merge, median, and quantile UDFS
    Adds reduce aggregates rule to reduce:
      median(x) -> tdigest_median(tdigest(x))
      quantile(q, x) -> tdigest_quantile(q, tdigest(x))
    Adds two-phase aggregate rule for tdigest

----


> Add TDigest functions for computing median and quantile
> -------------------------------------------------------
>
>                 Key: DRILL-4566
>                 URL: https://issues.apache.org/jira/browse/DRILL-4566
>             Project: Apache Drill
>          Issue Type: New Feature
>            Reporter: Steven Phillips
>            Assignee: Steven Phillips
>
> The tdigest library can be used by Drill to compute approximate value and 
> percentiles with using too much memory or spilling to disk, which would be 
> required to compute exactly.



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