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: Adding Scala version of PageRank example

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

(limited to 'examples/src/main/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)
+  }
+}
+
-- 
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