Get all vertexes with outDegree equals to 0 with GraphX

[Guillermo Ortiz]

I'm new with graphX. I need to get the vertex without out edges..
I guess that it's pretty easy but I did it pretty complicated.. and
inefficienct

val vertices: RDD[(VertexId, (List[String], List[String]))] =
  sc.parallelize(Array((1L, (List("a"), List[String]())),
    (2L, (List("b"), List[String]())),
    (3L, (List("c"), List[String]())),
    (4L, (List("d"), List[String]())),
    (5L, (List("e"), List[String]())),
    (6L, (List("f"), List[String]()))))

// Create an RDD for edges
val relationships: RDD[Edge[Boolean]] =
  sc.parallelize(Array(Edge(1L, 2L, true), Edge(2L, 3L, true),
Edge(3L, 4L, true), Edge(5L, 2L, true)))

val out = minGraph.outDegrees.map(vertex => vertex._1)

val finalVertexes = minGraph.vertices.keys.subtract(out)

//It must be something better than this way..
val nodes = finalVertexes.collect()
val result = minGraph.vertices.filter(v => nodes.contains(v._1))


What's the good way to do this operation? It seems that it should be
pretty easy.