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Posted to issues@spark.apache.org by "Sean Owen (JIRA)" <ji...@apache.org> on 2016/07/24 07:28:20 UTC
[jira] [Created] (SPARK-16694) Use for/foreach rather than map for
Unit expressions whose side effects are required
Sean Owen created SPARK-16694:
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Summary: 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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