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From "Jakob Bach (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (SPARK-21900) Numerical Error in simple Skewness Computation
Date Sun, 03 Sep 2017 09:52:00 GMT

    [ https://issues.apache.org/jira/browse/SPARK-21900?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16151760#comment-16151760
] 

Jakob Bach commented on SPARK-21900:
------------------------------------

Ok, thanks, my fault, I did not expected something like e-17 at the end of the truncated number,
but I rather assumed that the whole result was a number significantly greater than zero. Anyway,
I suppose this "bug" can be closed.

> Numerical Error in simple Skewness Computation
> ----------------------------------------------
>
>                 Key: SPARK-21900
>                 URL: https://issues.apache.org/jira/browse/SPARK-21900
>             Project: Spark
>          Issue Type: Bug
>          Components: SQL
>    Affects Versions: 2.2.0
>            Reporter: Jakob Bach
>            Priority: Minor
>
> The skewness() aggregate SQL function in the Scala implementation (org.apache.spark.sql.skewness)
seems to be buggy .The following code
> {code:java}
> import org.apache.spark.sql.functions
> import org.apache.spark.sql.SparkSession
> object SkewTest {
>   def main(args: Array[String]): Unit = {
>     val spark = SparkSession.
>       builder().
>       appName("Skewness example").
>       master("local[1]").
>       getOrCreate()
>     spark.createDataFrame(Seq(4,1,2,3).map(Tuple1(_))).agg(functions.skewness("_1")).show()
>   }
> }
> {code}
> should output 0 (as it does for Seq(1,2,3,4)), but outputs
> {code:none}
> +--------------------+
> |        skewness(_1)|
> +--------------------+
> |5.958081967793454...|
> +--------------------+
> {code}



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