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https://issues.apache.org/jira/browse/SPARK-21459?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Sean Owen resolved SPARK-21459.
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Resolution: Cannot Reproduce
> Some aggregation functions change the case of nested field names
> ----------------------------------------------------------------
>
> Key: SPARK-21459
> URL: https://issues.apache.org/jira/browse/SPARK-21459
> Project: Spark
> Issue Type: Bug
> Components: Spark Core
> Affects Versions: 1.6.0
> Reporter: David Allsopp
> Priority: Minor
>
> When working with DataFrames with nested schemas, the behavior of the
> aggregation functions is inconsistent with respect to preserving the case of
> the nested field names.
> For example, {{first()}} preserves the case of the field names, but
> {{collect_set()}} and {{collect_list()}} force the field names to lowercase.
> Expected behavior: Field name case is preserved (or is at least consistent
> and documented)
> Spark-shell session to reproduce:
> {code:java}
> case class Inner(Key:String, Value:String)
> case class Outer(ID:Long, Pairs:Array[Inner])
> val rdd = sc.parallelize(Seq(Outer(1L, Array(Inner("foo", "bar")))))
> val df = sqlContext.createDataFrame(rdd)
> scala> df
> ... = [ID: bigint, Pairs: array<struct<Key:string,Value:string>>]
> scala>df.groupBy("ID").agg(first("Pairs"))
> ... = [ID: bigint, first(Pairs)(): array<struct<Key:string,Value:string>>]
> // Note that Key and Value preserve their original case
> scala>df.groupBy("ID").agg(collect_set("Pairs"))
> ... = [ID: bigint, collect_set(Pairs): array<struct<key:string,value:string>>]
> // Note that key and value are now lowercased
> {code}
> Additionally, the column name (generated during aggregation) is inconsistent:
> {{first(Pairs)()}} versus {{collect_set(Pairs)}} - note the extra parentheses
> in the first name.
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