Graphx Example 1

triplets example: Students, Professor Relationship

import org.apache.spark._
import org.apache.spark.graphx._
import org.apache.spark.rdd.RDD

// Create an RDD for the vertices
val users: RDD[(VertexId, (String, String))] =
  sc.parallelize(Array((3L, ("rxin", "student")), (7L, ("jgonzal", "postdoc")),
                       (5L, ("franklin", "prof")), (2L, ("istoica", "prof")),
                       (4L, ("peter", "student"))))
// Create an RDD for edges
val relationships: RDD[Edge[String]] =
  sc.parallelize(Array(Edge(3L, 7L, "collab"),    Edge(5L, 3L, "advisor"),
                       Edge(2L, 5L, "colleague"), Edge(5L, 7L, "pi"),
                       Edge(4L, 0L, "student"),   Edge(5L, 0L, "colleague")))
// Define a default user in case there are relationship with missing user
val defaultUser = ("John Doe", "Missing")
// Build the initial Graph
// Note: Graph() is an abstract class
// While can not instantiate, you see no new key word
// but class methods of it can be invoked
// Therefore, this is what graph is for
val graph = Graph(users, relationships, defaultUser)
// Notice that there is a user 0 (for which we have no information) connected to users
// 4 (peter) and 5 (franklin).
graph.triplets.map(
  triplet => triplet.srcAttr._1 + " is the " + triplet.attr + " of " + triplet.dstAttr._1
).collect.foreach(println(_))
// Remove missing vertices as well as the edges to connected to them
val validGraph = graph.subgraph(vpred = (id, attr) => attr._2 != "Missing")
// The valid subgraph will disconnect users 4 and 5 by removing user 0
validGraph.vertices.collect.foreach(println(_))
validGraph.triplets.map(
  triplet => triplet.srcAttr._1 + " is the " + triplet.attr + " of " + triplet.dstAttr._1
).collect.foreach(println(_))

/*

Output:
istoica is the colleague of franklin
rxin is the collab of jgonzal
franklin is the advisor of rxin
peter is the student of John Doe
franklin is the colleague of John Doe
franklin is the pi of jgonzal

(4,(peter,student))
(2,(istoica,prof))
(3,(rxin,student))
(7,(jgonzal,postdoc))
(5,(franklin,prof))

istoica is the colleague of franklin
rxin is the collab of jgonzal
franklin is the advisor of rxin
franklin is the pi of jgonzal
*/