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https://issues.apache.org/jira/browse/SPARK-22725?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Sean Owen resolved SPARK-22725.
-------------------------------
    Resolution: Won't Fix

No follow up and not clear this is expected to work

> df.select on a Stream is broken, vs a List
> ------------------------------------------
>
>                 Key: SPARK-22725
>                 URL: https://issues.apache.org/jira/browse/SPARK-22725
>             Project: Spark
>          Issue Type: Bug
>          Components: Spark Core
>    Affects Versions: 2.3.0
>            Reporter: Andrew Ash
>            Priority: Minor
>
> See failing test at https://github.com/apache/spark/pull/19917
> Failing:
> {noformat}
>   test("SPARK-ABC123: support select with a splatted stream") {
>     val df = spark.createDataFrame(sparkContext.emptyRDD[Row], 
> StructType(List("bar", "foo").map {
>       StructField(_, StringType, false)
>     }))
>     val allColumns = Stream(df.col("bar"), col("foo"))
>     val result = df.select(allColumns : _*)
>   }
> {noformat}
> Succeeds:
> {noformat}
>   test("SPARK-ABC123: support select with a splatted stream") {
>     val df = spark.createDataFrame(sparkContext.emptyRDD[Row], 
> StructType(List("bar", "foo").map {
>       StructField(_, StringType, false)
>     }))
>     val allColumns = Seq(df.col("bar"), col("foo"))
>     val result = df.select(allColumns : _*)
>   }
> {noformat}
> After stepping through in a debugger, the difference manifests at 
> https://github.com/apache/spark/blob/8ae004b4602266d1f210e4c1564246d590412c06/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/plans/QueryPlan.scala#L120
> Changing {{seq.map}} to {{seq.toList.map}} causes the test to pass.
> I think there's a very subtle bug here where the {{Seq}} of column names 
> passed into {{select}} is expected to eagerly evaluate when {{.map}} is 
> called on it, even though that's not part of the {{Seq}} contract.



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