[jira] [Resolved] (SPARK-6480) histogram() bucket function is wrong in some simple edge cases

["Sean Owen (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/SPARK-6480?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Sean Owen resolved SPARK-6480.
------------------------------
       Resolution: Fixed
    Fix Version/s: 1.4.0
                   1.3.1
                   1.2.2

Resolved by https://github.com/apache/spark/pull/5148

> histogram() bucket function is wrong in some simple edge cases
> --------------------------------------------------------------
>
>                 Key: SPARK-6480
>                 URL: https://issues.apache.org/jira/browse/SPARK-6480
>             Project: Spark
>          Issue Type: Bug
>          Components: Spark Core
>    Affects Versions: 1.3.0
>            Reporter: Sean Owen
>            Assignee: Sean Owen
>             Fix For: 1.2.2, 1.3.1, 1.4.0
>
>
> (Credit to a customer report here) This test would fail now: 
> {code}
>     val rdd = sc.parallelize(Seq(1, 1, 1, 2, 3, 3))
>     assert(Array(3, 1, 2) === rdd.map(_.toDouble).histogram(3)._2)
> {code}
> Because it returns 3, 1, 0. The problem ultimately traces to the 'fast' bucket function that judges buckets based on a multiple of the gap between first and second elements. Errors multiply and the end of the final bucket fails to include the max.
> Fairly plausible use case actually.
> This can be tightened up easily with a slightly better expression. It will also fix this test, which is actually expecting the wrong answer:
> {code}
>     val rdd = sc.parallelize(6 to 99)
>     val (histogramBuckets, histogramResults) = rdd.histogram(9)
>     val expectedHistogramResults =
>       Array(11, 10, 11, 10, 10, 11, 10, 10, 11)
> {code}
> (Should be {{Array(11, 10, 10, 11, 10, 10, 11, 10, 11)}})



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