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+#
+# 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.
+#
+
+"""
+Randomly sampled RDDs.
+"""
+
+import sys
+
+from pyspark import SparkContext
+from pyspark.mllib.util import MLUtils
+
+
+if __name__ == "__main__":
+ if len(sys.argv) not in [1, 2]:
+ print >> sys.stderr, "Usage: sampled_rdds <libsvm data file>"
+ exit(-1)
+ if len(sys.argv) == 2:
+ datapath = sys.argv[1]
+ else:
+ datapath = 'data/mllib/sample_binary_classification_data.txt'
+
+ sc = SparkContext(appName="PythonSampledRDDs")
+
+ fraction = 0.1 # fraction of data to sample
+
+ examples = MLUtils.loadLibSVMFile(sc, datapath)
+ numExamples = examples.count()
+ if numExamples == 0:
+ print >> sys.stderr, "Error: Data file had no samples to load."
+ exit(1)
+ print 'Loaded data with %d examples from file: %s' % (numExamples, datapath)
+
+ # Example: RDD.sample() and RDD.takeSample()
+ expectedSampleSize = int(numExamples * fraction)
+ print 'Sampling RDD using fraction %g. Expected sample size = %d.' \
+ % (fraction, expectedSampleSize)
+ sampledRDD = examples.sample(withReplacement = True, fraction = fraction)
+ print ' RDD.sample(): sample has %d examples' % sampledRDD.count()
+ sampledArray = examples.takeSample(withReplacement = True, num = expectedSampleSize)
+ print ' RDD.takeSample(): sample has %d examples' % len(sampledArray)
+
+ print
+
+ # Example: RDD.sampleByKey()
+ keyedRDD = examples.map(lambda lp: (int(lp.label), lp.features))
+ print ' Keyed data using label (Int) as key ==> Orig'
+ # Count examples per label in original data.
+ keyCountsA = keyedRDD.countByKey()
+
+ # Subsample, and count examples per label in sampled data.
+ fractions = {}
+ for k in keyCountsA.keys():
+ fractions[k] = fraction
+ sampledByKeyRDD = keyedRDD.sampleByKey(withReplacement = True, fractions = fractions)
+ keyCountsB = sampledByKeyRDD.countByKey()
+ sizeB = sum(keyCountsB.values())
+ print ' Sampled %d examples using approximate stratified sampling (by label). ==> Sample' \
+ % sizeB
+
+ # Compare samples
+ print ' \tFractions of examples with key'
+ print 'Key\tOrig\tSample'
+ for k in sorted(keyCountsA.keys()):
+ fracA = keyCountsA[k] / float(numExamples)
+ if sizeB != 0:
+ fracB = keyCountsB.get(k, 0) / float(sizeB)
+ else:
+ fracB = 0
+ print '%d\t%g\t%g' % (k, fracA, fracB)
+
+ sc.stop()