questions about toArray and ClassTag

[wxhsdp <wx...@gmail.com>]

Hi, all
  i'am quite new in scala, i do some tests in spark shell

val b = a.mapPartitions{D => 
  val p = D.toArray
  .....
  p.toIterator
}

when a is an RDD of type RDD[Int], b.collect() works. but when i change a to
RDD[MyOwnType], b.collect() returns error:

14/04/20 10:14:46 ERROR OneForOneStrategy:
[L$line5.$read$$iwC$$iwC$$iwC$$iwC$InputMatrix;
java.lang.ArrayStoreException:
[L$line5.$read$$iwC$$iwC$$iwC$$iwC$InputMatrix;
	at scala.runtime.ScalaRunTime$.array_update(ScalaRunTime.scala:88)

i figure out the question is about toArray
def toArray[B >: A](implicit arg0: ClassTag[B]): Array[B]
an array containing all elements of this traversable or iterator. An
ClassTag must be available for the element type of this traversable or
iterator.

but i do not know how to do this, how to define an ClassTag, and give it to
toArray? i tried to set implicit 
arg0 like this:
val p = D.toArray(classTag[MyOwnType])
but it doesn't work

thanks for your help




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