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https://issues.apache.org/jira/browse/SPARK-25976?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16680938#comment-16680938
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Yuval Yaari commented on SPARK-25976:
-------------------------------------
correct, however in scala there is not much performance penalty on asking
isEmpty.
i suggest:
{code:java}
> sc.emptyRDD[Double]().reduce(_ + _)
java.lang.UnsupportedOperationException("empty collection")
> sc.emptyRDD[Double]().reduce(_ + _, () => Double.NaN)
Double.NaN
{code}
> Allow rdd.reduce on empty rdd by returning an Option[T]
> -------------------------------------------------------
>
> Key: SPARK-25976
> URL: https://issues.apache.org/jira/browse/SPARK-25976
> Project: Spark
> Issue Type: Improvement
> Components: Spark Core
> Affects Versions: 2.3.2
> Reporter: Yuval Yaari
> Priority: Minor
>
> it is sometimes useful to let the user decide what value to return when
> reducing on an empty rdd.
> currently, if there is no data to reduce an UnsupportedOperationException is
> thrown.
> although user can catch that exception, it seems like a "shaky" solution as
> UnsupportedOperationException might be thrown from a different location.
> Instead, we can overload the reduce method by adding add a new method:
> reduce(f: (T, T) => T, defaultIfEmpty: () => T): T
> the reduce API will not be effected as it will simply call the second reduce
> method throwing an UnsupportedException as the default value
>
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