found the missing SSSP

src/main/scala/com/databricks/apps/graphx/sssp.scala

@@ -0,0 +1,33 @@
+// SSSP impl in Graphx using Pregel
+//https://en.wikipedia.org/wiki/Dijkstra%27s_algorithm
+//http://spark.apache.org/docs/latest/graphx-programming-guide.html#pregel-api
+//http://stackoverflow.com/questions/23700124/how-to-get-sssp-actual-path-by-apache-spark-graphx
+
+import org.apache.spark.graphx._
+import org.apache.spark.graphx.util.GraphGenerators
+
+val graph = GraphGenerators.logNormalGraph(sc, numVertices = 5, numEParts = sc.defaultParallelism, mu = 4.0, sigma = 1.3).mapEdges(e => e.attr.toDouble)
+graph.edges.foreach(println)
+
+// initialize all vertices except the root to have distance infinity
+val sourceId: VertexId = 0
+val initialGraph : Graph[(Double, List[VertexId]), Double] = graph.mapVertices((id, _) => if (id == sourceId) (0.0, List[VertexId](sourceId)) else (Double.PositiveInfinity, List[VertexId]()))
+
+val sssp = initialGraph.pregel((Double.PositiveInfinity, List[VertexId]()), Int.MaxValue, EdgeDirection.Out)(
+  // vertex program
+  (id, dist, newDist) => if (dist._1 < newDist._1) dist else newDist, 
+
+  // send message
+  triplet => {
+    if (triplet.srcAttr._1 < triplet.dstAttr._1 - triplet.attr ) {
+      Iterator((triplet.dstId, (triplet.srcAttr._1 + triplet.attr , triplet.srcAttr._2 :+ triplet.dstId)))
+    } else {
+      Iterator.empty
+    }
+  },
+
+  // merge message
+  (a, b) => if (a._1 < b._1) a else b)
+
+  println(sssp.vertices.collect.mkString("\n")
+)