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https://issues.apache.org/jira/browse/SPARK-22208?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16333678#comment-16333678
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Sean Owen commented on SPARK-22208:
-----------------------------------
It's a bug fix, and more of a corner case of behavior, so I don't know if it
must be called out in the release notes as a behavior change, if that's what
you mean.
> Improve percentile_approx by not rounding up targetError and starting from
> index 0
> ----------------------------------------------------------------------------------
>
> Key: SPARK-22208
> URL: https://issues.apache.org/jira/browse/SPARK-22208
> Project: Spark
> Issue Type: Improvement
> Components: SQL
> Affects Versions: 2.3.0
> Reporter: Zhenhua Wang
> Assignee: Zhenhua Wang
> Priority: Major
> Labels: releasenotes
> Fix For: 2.3.0
>
>
> percentile_approx never returns the first element when percentile is in
> (relativeError, 1/N], where relativeError default is 1/10000, and N is the
> total number of elements. But ideally, percentiles in [0, 1/N] should all
> return the first element as the answer.
> For example, given input data 1 to 10, if a user queries 10% (or even less)
> percentile, it should return 1, because the first value 1 already reaches
> 10%. Currently it returns 2.
> Based on the paper, targetError is not rounded up, and searching index should
> start from 0 instead of 1. By following the paper, we should be able to fix
> the cases mentioned above.
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