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https://issues.apache.org/jira/browse/SPARK-16694?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15390982#comment-15390982
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Apache Spark commented on SPARK-16694:
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User 'srowen' has created a pull request for this issue:
https://github.com/apache/spark/pull/14332
> Use for/foreach rather than map for Unit expressions whose side effects are
> required
> ------------------------------------------------------------------------------------
>
> Key: SPARK-16694
> URL: https://issues.apache.org/jira/browse/SPARK-16694
> Project: Spark
> Issue Type: Improvement
> Components: Examples, MLlib, Spark Core, SQL, Streaming
> Reporter: Sean Owen
> Assignee: Sean Owen
> Priority: Minor
>
> {{map}} is misused in many places where {{foreach}} is intended. This caused
> a bug in https://issues.apache.org/jira/browse/SPARK-16664 and might be a
> latent bug elsewhere; it's also easy to find with IJ inspections. Worth
> patching up.
> To illustrate the general problem, {{map}} happens to work in Scala where the
> collection isn't lazy, but will fail to execute the code when it is. {{map}}
> also causes a collection of {{Unit}} to be created pointlessly.
> {code}
> scala> val foo = Seq(1,2,3)
> foo: Seq[Int] = List(1, 2, 3)
> scala> foo.map(println)
> 1
> 2
> 3
> res0: Seq[Unit] = List((), (), ())
> scala> foo.view.map(println)
> res1: scala.collection.SeqView[Unit,Seq[_]] = SeqViewM(...)
> scala> foo.view.foreach(println)
> 1
> 2
> 3
> {code}
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