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https://issues.apache.org/jira/browse/SPARK-12823?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15829810#comment-15829810
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Wenchen Fan commented on SPARK-12823:
-------------------------------------
When your data are loaded into `DataFrame`, the type information is removed. We
don't know where the struct type column comes from, `case class KV`? `case
class Row`? `Tuple2`? We don't care, because in `DataFrame`, the object type of
struct type column is always `Row`.
This means, if you write a UDF for a struct type column, the parameter type
must be `Row`.
If you do wanna keep the type information, please use Dataset. For your
example, you can write
{code}
case class KV(key: Long, value: String)
case class Row(kv: KV)
val ds: Dataset[Row] = sc.parallelize(List(Row(KV(1L, "a")), Row(KV(5L,
"b")))).toDS
ds.map(_.kv.value).show
{code}
> Cannot create UDF with StructType input
> ---------------------------------------
>
> Key: SPARK-12823
> URL: https://issues.apache.org/jira/browse/SPARK-12823
> Project: Spark
> Issue Type: Bug
> Components: SQL
> Affects Versions: 1.5.2
> Reporter: Frank Rosner
>
> h5. Problem
> It is not possible to apply a UDF to a column that has a struct data type.
> Two previous requests to the mailing list remained unanswered.
> h5. How-To-Reproduce
> {code}
> val sql = new org.apache.spark.sql.SQLContext(sc)
> import sql.implicits._
> case class KV(key: Long, value: String)
> case class Row(kv: KV)
> val df = sc.parallelize(List(Row(KV(1L, "a")), Row(KV(5L, "b")))).toDF
> val udf1 = org.apache.spark.sql.functions.udf((kv: KV) => kv.value)
> df.select(udf1(df("kv"))).show
> // java.lang.ClassCastException:
> org.apache.spark.sql.catalyst.expressions.GenericRowWithSchema cannot be cast
> to $line78.$read$$iwC$$iwC$KV
> val udf2 = org.apache.spark.sql.functions.udf((kv: (Long, String)) => kv._2)
> df.select(udf2(df("kv"))).show
> // org.apache.spark.sql.AnalysisException: cannot resolve 'UDF(kv)' due to
> data type mismatch: argument 1 requires struct<_1:bigint,_2:string> type,
> however, 'kv' is of struct<key:bigint,value:string> type.;
> {code}
> h5. Mailing List Entries
> -
> https://mail-archives.apache.org/mod_mbox/spark-user/201511.mbox/%3CCACUahd8M=ipCbFCYDyein_=vqyoantn-tpxe6sq395nh10g...@mail.gmail.com%3E
> - https://www.mail-archive.com/[email protected]/msg43092.html
> h5. Possible Workaround
> If you create a {{UserDefinedFunction}} manually, not using the {{udf}}
> helper functions, it works. See https://github.com/FRosner/struct-udf, which
> exposes the {{UserDefinedFunction}} constructor (public from package
> private). However, then you have to work with a {{Row}}, because it does not
> automatically convert the row to a case class / tuple.
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