Optimize Scala PageRank to use reduceByKey

examples/src/main/scala/spark/examples/SparkPageRank.scala

@@ -20,9 +20,10 @@ object SparkPageRank {
       System.exit(1)
     }
     var iters = args(2).toInt
-    val ctx = new SparkContext(args(0), "PageRank", System.getenv("SPARK_HOME"), Seq(System.getenv("SPARK_EXAMPLES_JAR")))
+    val ctx = new SparkContext(args(0), "PageRank",
+      System.getenv("SPARK_HOME"), Seq(System.getenv("SPARK_EXAMPLES_JAR")))
     val lines = ctx.textFile(args(1), 1)
-    val links = lines.map{s =>
+    val links = lines.map{ s =>
       val parts = s.split("\\s+")
       (parts(0), parts(1))
     }.distinct().groupByKey().cache()
@@ -33,17 +34,12 @@ object SparkPageRank {
         val size = urls.size
         urls.map(url => (url, rank / size))
       }
-
-      ranks = contribs.groupByKey().mapValues{ranks =>
-        val sumRanks = ranks.foldLeft(0.0)(_ + _)
-        0.15 + sumRanks * 0.85
-      }
+      ranks = contribs.reduceByKey(_ + _).mapValues(0.15 + 0.85 * _)
     }
 
     val output = ranks.collect()
     output.foreach(tup => println(tup._1 + " has rank: " + tup._2 + "."))
 
-    ctx.stop()
     System.exit(0)
   }
 }