From 76077bf9f4b726699ba9e59cdfa9c4361df4ea92 Mon Sep 17 00:00:00 2001
From: Andre Schumacher <schumach@icsi.berkeley.edu>
Date: Tue, 20 Aug 2013 13:22:06 -0700
Subject: Implementing SPARK-838: Add DoubleRDDFunctions methods to PySpark

---
 python/pyspark/rdd.py | 60 ++++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 59 insertions(+), 1 deletion(-)

(limited to 'python/pyspark/rdd.py')

diff --git a/python/pyspark/rdd.py b/python/pyspark/rdd.py
index 99f5967a8e..1e9b3bb5c0 100644
--- a/python/pyspark/rdd.py
+++ b/python/pyspark/rdd.py
@@ -31,6 +31,7 @@ from pyspark.serializers import batched, Batch, dump_pickle, load_pickle, \
     read_from_pickle_file
 from pyspark.join import python_join, python_left_outer_join, \
     python_right_outer_join, python_cogroup
+from pyspark.statcounter import StatCounter
 
 from py4j.java_collections import ListConverter, MapConverter
 
@@ -357,6 +358,63 @@ class RDD(object):
         3
         """
         return self.mapPartitions(lambda i: [sum(1 for _ in i)]).sum()
+    
+    def stats(self):
+        """
+        Return a L{StatCounter} object that captures the mean, variance
+        and count of the RDD's elements in one operation.
+        """
+        def redFunc(left_counter, right_counter):
+            return left_counter.mergeStats(right_counter)
+
+        return self.mapPartitions(lambda i: [StatCounter(i)]).reduce(redFunc)
+
+    def mean(self):
+        """
+        Compute the mean of this RDD's elements.
+
+        >>> sc.parallelize([1, 2, 3]).mean()
+        2.0
+        """
+        return self.stats().mean()
+
+    def variance(self):
+        """
+        Compute the variance of this RDD's elements.
+
+        >>> sc.parallelize([1, 2, 3]).variance()
+        0.666...
+        """
+        return self.stats().variance()
+
+    def stdev(self):
+        """
+        Compute the standard deviation of this RDD's elements.
+
+        >>> sc.parallelize([1, 2, 3]).stdev()
+        0.816...
+        """
+        return self.stats().stdev()
+  
+    def sampleStdev(self):
+        """
+        Compute the sample standard deviation of this RDD's elements (which corrects for bias in
+        estimating the standard deviation by dividing by N-1 instead of N).
+
+        >>> sc.parallelize([1, 2, 3]).sampleStdev()
+        1.0
+        """
+        return self.stats().sampleStdev()
+
+    def sampleVariance(self):
+        """
+        Compute the sample variance of this RDD's elements (which corrects for bias in
+        estimating the variance by dividing by N-1 instead of N).
+
+        >>> sc.parallelize([1, 2, 3]).sampleVariance()
+        1.0
+        """
+        return self.stats().sampleVariance()
 
     def countByValue(self):
         """
@@ -777,7 +835,7 @@ def _test():
     # The small batch size here ensures that we see multiple batches,
     # even in these small test examples:
     globs['sc'] = SparkContext('local[4]', 'PythonTest', batchSize=2)
-    (failure_count, test_count) = doctest.testmod(globs=globs)
+    (failure_count, test_count) = doctest.testmod(globs=globs,optionflags=doctest.ELLIPSIS)
     globs['sc'].stop()
     if failure_count:
         exit(-1)
-- 
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