小编sou*_*abh的帖子

collectAsListSpark DataFrame API 的方法返回 ajava.util.List而不是 Scala 列表有什么具体原因吗？

我试图从包含scala函数定义的字符串中定义spark(2.0)中的udf.这是片段:

val universe: scala.reflect.runtime.universe.type = scala.reflect.runtime.universe
import universe._
import scala.reflect.runtime.currentMirror
import scala.tools.reflect.ToolBox
val toolbox = currentMirror.mkToolBox()
val f = udf(toolbox.eval(toolbox.parse("(s:String) => 5")).asInstanceOf[String => Int])
sc.parallelize(Seq("1","5")).toDF.select(f(col("value"))).show

这给了我一个错误:

  Caused by: java.lang.ClassCastException: cannot assign instance of scala.collection.immutable.List$SerializationProxy to field org.apache.spark.rdd.RDD.org$apache$spark$rdd$RDD$$dependencies_ of type scala.collection.Seq in instance of org.apache.spark.rdd.MapPartitionsRDD
   at java.io.ObjectStreamClass$FieldReflector.setObjFieldValues(ObjectStreamClass.java:2133)
   at java.io.ObjectStreamClass.setObjFieldValues(ObjectStreamClass.java:1305)
   at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:2024)
   at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:1942)
   at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1808)
   at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1353)
   at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:2018)
   at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:1942)
   at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1808)
   at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1353)
   at java.io.ObjectInputStream.readObject(ObjectInputStream.java:373)
   at org.apache.spark.serializer.JavaDeserializationStream.readObject(JavaSerializer.scala:75)
   at org.apache.spark.serializer.JavaSerializerInstance.deserialize(JavaSerializer.scala:114)
   at org.apache.spark.scheduler.ResultTask.runTask(ResultTask.scala:66)
   at org.apache.spark.scheduler.Task.run(Task.scala:85)
   at org.apache.spark.executor.Executor$TaskRunner.run(Executor.scala:274)
   at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
   at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) …