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https://issues.apache.org/jira/browse/SPARK-26021?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17027280#comment-17027280
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Dongjoon Hyun commented on SPARK-26021:
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Is that backported or marked as correctness issue?
> -0.0 and 0.0 not treated consistently, doesn't match Hive
> ---------------------------------------------------------
>
> Key: SPARK-26021
> URL: https://issues.apache.org/jira/browse/SPARK-26021
> Project: Spark
> Issue Type: Bug
> Components: SQL
> Affects Versions: 2.4.0
> Reporter: Sean R. Owen
> Assignee: Alon Doron
> Priority: Critical
> Labels: correctness
> Fix For: 3.0.0
>
>
> Per [~adoron] and [~mccheah] and SPARK-24834, I'm splitting this out as a new
> issue:
> The underlying issue is how Spark and Hive treat 0.0 and -0.0, which are
> numerically identical but not the same double value:
> In hive, 0.0 and -0.0 are equal since
> https://issues.apache.org/jira/browse/HIVE-11174.
> That's not the case with spark sql as "group by" (non-codegen) treats them
> as different values. Since their hash is different they're put in different
> buckets of UnsafeFixedWidthAggregationMap.
> In addition there's an inconsistency when using the codegen, for example the
> following unit test:
> {code:java}
> println(Seq(0.0d, 0.0d,
> -0.0d).toDF("i").groupBy("i").count().collect().mkString(", "))
> {code}
> [0.0,3]
> {code:java}
> println(Seq(0.0d, -0.0d,
> 0.0d).toDF("i").groupBy("i").count().collect().mkString(", "))
> {code}
> [0.0,1], [-0.0,2]
> {code:java}
> spark.conf.set("spark.sql.codegen.wholeStage", "false")
> println(Seq(0.0d, -0.0d,
> 0.0d).toDF("i").groupBy("i").count().collect().mkString(", "))
> {code}
> [0.0,2], [-0.0,1]
> Note that the only difference between the first 2 lines is the order of the
> elements in the Seq.
> This inconsistency is resulted by different partitioning of the Seq and the
> usage of the generated fast hash map in the first, partial, aggregation.
> It looks like we need to add a specific check for -0.0 before hashing (both
> in codegen and non-codegen modes) if we want to fix this.
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