Merge pull request #802 from stayhf/SPARK-760-Python

Simple PageRank algorithm implementation in Python for SPARK-760

python/examples/pagerank.py

+#
+# Licensed to the Apache Software Foundation (ASF) under one or more
+# contributor license agreements.  See the NOTICE file distributed with
+# this work for additional information regarding copyright ownership.
+# The ASF licenses this file to You under the Apache License, Version 2.0
+# (the "License"); you may not use this file except in compliance with
+# the License.  You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+#!/usr/bin/env python
+
+import re, sys
+from operator import add
+
+from pyspark import SparkContext
+
+
+def computeContribs(urls, rank):
+    """Calculates URL contributions to the rank of other URLs."""
+    num_urls = len(urls)
+    for url in urls: yield (url, rank / num_urls)
+
+
+def parseNeighbors(urls):
+    """Parses a urls pair string into urls pair."""
+    parts = re.split(r'\s+', urls)
+    return parts[0], parts[1]
+
+
+if __name__ == "__main__":
+    if len(sys.argv) < 3:
+        print >> sys.stderr, "Usage: pagerank <master> <file> <number_of_iterations>"
+        exit(-1)
+
+    # Initialize the spark context.
+    sc = SparkContext(sys.argv[1], "PythonPageRank")
+
+    # Loads in input file. It should be in format of:
+    #     URL         neighbor URL
+    #     URL         neighbor URL
+    #     URL         neighbor URL
+    #     ...
+    lines = sc.textFile(sys.argv[2], 1)
+
+    # Loads all URLs from input file and initialize their neighbors.
+    links = lines.map(lambda urls: parseNeighbors(urls)).distinct().groupByKey().cache()
+
+    # Loads all URLs with other URL(s) link to from input file and initialize ranks of them to one.
+    ranks = links.map(lambda (url, neighbors): (url, 1.0))
+
+    # Calculates and updates URL ranks continuously using PageRank algorithm.
+    for iteration in xrange(int(sys.argv[3])):
+        # Calculates URL contributions to the rank of other URLs.
+        contribs = links.join(ranks).flatMap(lambda (url, (urls, rank)):
+            computeContribs(urls, rank))
+
+        # Re-calculates URL ranks based on neighbor contributions.
+        ranks = contribs.reduceByKey(add).mapValues(lambda rank: rank * 0.85 + 0.15)
+
+    # Collects all URL ranks and dump them to console.
+    for (link, rank) in ranks.collect():
+        print "%s has rank: %s." % (link, rank)