Fix Pregel SSSP example in programming guide

docs/graphx-programming-guide.md

@@ -511,7 +511,7 @@ In the following example we use the `mapReduceTriplets` operator to compute the
 more senior followers of each user.
 
 {% highlight scala %}
-// Import Random graph generation library
+// Import random graph generation library
 import org.apache.spark.graphx.util.GraphGenerators
 // Create a graph with "age" as the vertex property.  Here we use a random graph for simplicity.
 val graph: Graph[Double, Int] =
@@ -643,18 +643,23 @@ iterations, and the edge direction in which to send messages (by default along o
 second argument list contains the user defined functions for receiving messages (the vertex program
 `vprog`), computing messages (`sendMsg`), and combining messages `mergeMsg`.
 
-We can use the Pregel operator to express computation such single source shortest path in the
-following example.
+We can use the Pregel operator to express computation such as single source
+shortest path in the following example.
 
 {% highlight scala %}
-val graph: Graph[String, Double] // A graph with edge attributes containing distances
-val sourceId: VertexId = 42 // The ultimate source
+import org.apache.spark.graphx._
+// Import random graph generation library
+import org.apache.spark.graphx.util.GraphGenerators
+// A graph with edge attributes containing distances
+val graph: Graph[Int, Double] =
+  GraphGenerators.logNormalGraph(sc, numVertices = 100).mapEdges(e => e.attr.toDouble)
+val sourceId: VertexID = 42 // The ultimate source
 // Initialize the graph such that all vertices except the root have distance infinity.
-val initialGraph = graph.mapVertices((id, _) => if (id == shourceId) 0.0 else Double.PositiveInfinity)
+val initialGraph = graph.mapVertices((id, _) => if (id == sourceId) 0.0 else Double.PositiveInfinity)
 val sssp = initialGraph.pregel(Double.PositiveInfinity)(
-  (id, dist, newDist) => math.min(dist, newDist) // Vertex Program
+  (id, dist, newDist) => math.min(dist, newDist), // Vertex Program
   triplet => {  // Send Message
-    if(triplet.srcAttr + triplet.attr < triplet.dstAttr) {
+    if (triplet.srcAttr + triplet.attr < triplet.dstAttr) {
       Iterator((triplet.dstId, triplet.srcAttr + triplet.attr))
     } else {
       Iterator.empty
@@ -662,6 +667,7 @@ val sssp = initialGraph.pregel(Double.PositiveInfinity)(
   },
   (a,b) => math.min(a,b) // Merge Message
   )
+println(sssp.vertices.collect.mkString("\n"))
 {% endhighlight %}
 
 # Graph Builders