Scala FoldLeft: object RDD does not take type parameters

Question

I'm trying to apply foldLeft to list of Strings as following:

 items.foldLeft(RDD[(String, Iterable[SomeClass])])((total, item) => total.union(fetchRDD(item))

where:

• item is a List[String]
• SomeClass is a simple case Class

But I receive the following exception for "RDD[(String, Iterable[SomeClass])]"-(expression in first braces of foldLeft):

"object RDD does not take type parameters"

But I receive the following exception for "RDD[(String, Iterable[WikipediaArticle])]"-(expression in first braces of foldLeft):

"object RDD does not take type parameters" - .

Answer 1

You have to pass an instance of type RDD[_] as first parameter in foldLeft .

Here you are passing the object RDD which as the error says does not take type parameters.

You likely want to add () like RDD[X]() to create an empty RDD and use it as the zero element in the foldLeft .