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https://issues.apache.org/jira/browse/SPARK-25976?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16680889#comment-16680889
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Hyukjin Kwon edited comment on SPARK-25976 at 11/9/18 5:29 AM:
---------------------------------------------------------------
Can you describe expected input and output?
Scala itself does not allow:
{code}
scala> Seq[Int]().reduce(_ + _)
java.lang.UnsupportedOperationException: empty.reduceLeft
at
scala.collection.LinearSeqOptimized$class.reduceLeft(LinearSeqOptimized.scala:137)
at scala.collection.immutable.List.reduceLeft(List.scala:84)
at scala.collection.TraversableOnce$class.reduce(TraversableOnce.scala:208)
at scala.collection.AbstractTraversable.reduce(Traversable.scala:104)
... 49 elided
{code}
I don't think we should fix this.
was (Author: hyukjin.kwon):
Can you describe expected input and output?
Scala itself does not allow:
{code}
scala> Seq().reduce(_ + _)
<console>:12: error: missing parameter type for expanded function ((x$1:
<error>, x$2) => x$1.$plus(x$2))
Seq().reduce(_ + _)
^
<console>:12: error: missing parameter type for expanded function ((x$1:
<error>, x$2: <error>) => x$1.$plus(x$2))
Seq().reduce(_ + _)
^
{code}
I don't think we should fix this.
> 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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