From cce758b8938afb24c6d61a02f697201c41801fb6 Mon Sep 17 00:00:00 2001
From: Nick Pentreath <nick.pentreath@gmail.com>
Date: Wed, 7 Aug 2013 16:38:52 +0200
Subject: [PATCH 1/2] Adding Scala version of PageRank example

---
 .../scala/spark/examples/SparkPageRank.scala  | 51 +++++++++++++++++++
 1 file changed, 51 insertions(+)
 create mode 100644 examples/src/main/scala/spark/examples/SparkPageRank.scala

diff --git a/examples/src/main/scala/spark/examples/SparkPageRank.scala b/examples/src/main/scala/spark/examples/SparkPageRank.scala
new file mode 100644
index 0000000000..6d2be34956
--- /dev/null
+++ b/examples/src/main/scala/spark/examples/SparkPageRank.scala
@@ -0,0 +1,51 @@
+package spark.examples
+
+import spark.SparkContext._
+import spark.SparkContext
+
+
+/**
+ * Computes the PageRank of URLs from an input file. Input file should
+ * be in format of:
+ * URL         neighbor URL
+ * URL         neighbor URL
+ * URL         neighbor URL
+ * ...
+ * where URL and their neighbors are separated by space(s).
+ */
+object SparkPageRank {
+
+  def main(args: Array[String]) {
+    if (args.length < 3) {
+      System.err.println("Usage: PageRank <master> <file> <number_of_iterations>")
+      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 lines = ctx.textFile(args(1), 1)
+    val links = lines.map(s => {
+        val parts = s.split("\\s+")
+        (parts(0), parts(1))
+      }).distinct().groupByKey().cache()
+    var ranks = links.mapValues(v => 1.0)
+
+    for (i <- 1 to iters) {
+      val contribs = links.join(ranks).values.flatMap{ case (urls, rank) => {
+        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
+      })
+    }
+
+    val output = ranks.collect()
+    output.foreach(tup => println(tup._1 + " has rank: " + tup._2 + "."))
+
+    ctx.stop()
+    System.exit(0)
+  }
+}
+

From c4eea875ac5d02b46b22b454532c9702c3fa6240 Mon Sep 17 00:00:00 2001
From: Nick Pentreath <nick.pentreath@gmail.com>
Date: Thu, 8 Aug 2013 12:40:37 +0200
Subject: [PATCH 2/2] Style changes as per Matei's comments

---
 .../scala/spark/examples/SparkPageRank.scala    | 17 ++++++++---------
 1 file changed, 8 insertions(+), 9 deletions(-)

diff --git a/examples/src/main/scala/spark/examples/SparkPageRank.scala b/examples/src/main/scala/spark/examples/SparkPageRank.scala
index 6d2be34956..4e41c026a4 100644
--- a/examples/src/main/scala/spark/examples/SparkPageRank.scala
+++ b/examples/src/main/scala/spark/examples/SparkPageRank.scala
@@ -14,7 +14,6 @@ import spark.SparkContext
  * where URL and their neighbors are separated by space(s).
  */
 object SparkPageRank {
-
   def main(args: Array[String]) {
     if (args.length < 3) {
       System.err.println("Usage: PageRank <master> <file> <number_of_iterations>")
@@ -23,22 +22,22 @@ object SparkPageRank {
     var iters = args(2).toInt
     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 parts = s.split("\\s+")
-        (parts(0), parts(1))
-      }).distinct().groupByKey().cache()
+    val links = lines.map{s =>
+      val parts = s.split("\\s+")
+      (parts(0), parts(1))
+    }.distinct().groupByKey().cache()
     var ranks = links.mapValues(v => 1.0)
 
     for (i <- 1 to iters) {
-      val contribs = links.join(ranks).values.flatMap{ case (urls, rank) => {
+      val contribs = links.join(ranks).values.flatMap{ case (urls, rank) =>
         val size = urls.size
         urls.map(url => (url, rank / size))
-      }}
+      }
 
-      ranks = contribs.groupByKey().mapValues(ranks => {
+      ranks = contribs.groupByKey().mapValues{ranks =>
         val sumRanks = ranks.foldLeft(0.0)(_ + _)
         0.15 + sumRanks * 0.85
-      })
+      }
     }
 
     val output = ranks.collect()