[jira] [Created] (SPARK-18884) Support Array[_] in ScalaUDF

["Takeshi Yamamuro (JIRA)" <ji...@apache.org>]

Takeshi Yamamuro created SPARK-18884:
----------------------------------------

             Summary: Support Array[_] in ScalaUDF
                 Key: SPARK-18884
                 URL: https://issues.apache.org/jira/browse/SPARK-18884
             Project: Spark
          Issue Type: Bug
          Components: SQL
    Affects Versions: 2.0.2
            Reporter: Takeshi Yamamuro
            Priority: Minor


Throw an exception if we use `Array[_]` in `ScalaUDF`;

{code}
scala> import org.apache.spark.sql.execution.debug._
scala> Seq((0, 1)).toDF("a", "b").select(array($"a", $"b").as("ar")).write.mode("overwrite").parquet("/Users/maropu/Desktop/data/")
scala> val df = spark.read.load("/Users/maropu/Desktop/data/")
scala> val df = Seq((0, 1)).toDF("a", "b").select(array($"a", $"b").as("ar"))
scala> val testArrayUdf = udf { (ar: Array[Int]) => ar.sum }
scala> df.select(testArrayUdf($"ar")).show

Caused by: java.lang.ClassCastException: scala.collection.mutable.WrappedArray$ofRef cannot be cast to [I
  at $anonfun$1.apply(<console>:23)
  at org.apache.spark.sql.catalyst.expressions.ScalaUDF$$anonfun$2.apply(ScalaUDF.scala:89)
  at org.apache.spark.sql.catalyst.expressions.ScalaUDF$$anonfun$2.apply(ScalaUDF.scala:88)
  at org.apache.spark.sql.catalyst.expressions.ScalaUDF.eval(ScalaUDF.scala:1069)
  ... 99 more
{code}

On the other hand, the query below is passed;

{code}
scala> val testSeqUdf = udf { (ar: Seq[Int]) => ar.sum }
scala> df.select(testSeqUdf($"ar")).show
+-------+
|UDF(ar)|
+-------+
|      1|
+-------+
{code}

I'm not sure this behivour is an expected one. The curernt implementation querys argument types (`DataType`)
by reflection (`ScalaReflection.schemaFor`) in `sql.functions.udf`, and then creates type converters (`CatalystTypeConverters`) from the types.
`Seq[_]` and `Array[_]` are represented as `ArrayType` in `DataType` and both types are handled by using `ArrayConverter.
However, since we cannot tell a difference between both types in `DataType`, ISTM it's difficut to support the two array types
based on this current design.
One idea (of curse, it's not the best) I have is to create type converters directly from `TypeTag` in `sql.functions.udf`.
This is a prototype (https://github.com/apache/spark/compare/master...maropu:ArrayTypeUdf#diff-89643554d9757dd3e91abff1cc6096c7R740) to
support both array types in `ScalaUDF`. I'm not sure this is acceptable and welcome any suggestion.



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