diff options
Diffstat (limited to 'python/pyspark/rdd.py')
| -rw-r--r-- | python/pyspark/rdd.py | 99 |
1 files changed, 92 insertions, 7 deletions
diff --git a/python/pyspark/rdd.py b/python/pyspark/rdd.py index 1e9b3bb5c0..914118ccdd 100644 --- a/python/pyspark/rdd.py +++ b/python/pyspark/rdd.py @@ -21,6 +21,7 @@ from collections import defaultdict from itertools import chain, ifilter, imap, product import operator import os +import sys import shlex from subprocess import Popen, PIPE from tempfile import NamedTemporaryFile @@ -32,6 +33,7 @@ from pyspark.serializers import batched, Batch, dump_pickle, load_pickle, \ from pyspark.join import python_join, python_left_outer_join, \ python_right_outer_join, python_cogroup from pyspark.statcounter import StatCounter +from pyspark.rddsampler import RDDSampler from py4j.java_collections import ListConverter, MapConverter @@ -165,14 +167,60 @@ class RDD(object): .reduceByKey(lambda x, _: x) \ .map(lambda (x, _): x) - # TODO: sampling needs to be re-implemented due to Batch - #def sample(self, withReplacement, fraction, seed): - # jrdd = self._jrdd.sample(withReplacement, fraction, seed) - # return RDD(jrdd, self.ctx) + def sample(self, withReplacement, fraction, seed): + """ + Return a sampled subset of this RDD (relies on numpy and falls back + on default random generator if numpy is unavailable). + + >>> sc.parallelize(range(0, 100)).sample(False, 0.1, 2).collect() #doctest: +SKIP + [2, 3, 20, 21, 24, 41, 42, 66, 67, 89, 90, 98] + """ + return self.mapPartitionsWithSplit(RDDSampler(withReplacement, fraction, seed).func, True) + + # this is ported from scala/spark/RDD.scala + def takeSample(self, withReplacement, num, seed): + """ + Return a fixed-size sampled subset of this RDD (currently requires numpy). + + >>> sc.parallelize(range(0, 10)).takeSample(True, 10, 1) #doctest: +SKIP + [4, 2, 1, 8, 2, 7, 0, 4, 1, 4] + """ + + fraction = 0.0 + total = 0 + multiplier = 3.0 + initialCount = self.count() + maxSelected = 0 + + if (num < 0): + raise ValueError + + if initialCount > sys.maxint - 1: + maxSelected = sys.maxint - 1 + else: + maxSelected = initialCount + + if num > initialCount and not withReplacement: + total = maxSelected + fraction = multiplier * (maxSelected + 1) / initialCount + else: + fraction = multiplier * (num + 1) / initialCount + total = num - #def takeSample(self, withReplacement, num, seed): - # vals = self._jrdd.takeSample(withReplacement, num, seed) - # return [load_pickle(bytes(x)) for x in vals] + samples = self.sample(withReplacement, fraction, seed).collect() + + # If the first sample didn't turn out large enough, keep trying to take samples; + # this shouldn't happen often because we use a big multiplier for their initial size. + # See: scala/spark/RDD.scala + while len(samples) < total: + if seed > sys.maxint - 2: + seed = -1 + seed += 1 + samples = self.sample(withReplacement, fraction, seed).collect() + + sampler = RDDSampler(withReplacement, fraction, seed+1) + sampler.shuffle(samples) + return samples[0:total] def union(self, other): """ @@ -754,6 +802,43 @@ class RDD(object): """ return python_cogroup(self, other, numPartitions) + def subtractByKey(self, other, numPartitions=None): + """ + Return each (key, value) pair in C{self} that has no pair with matching key + in C{other}. + + >>> x = sc.parallelize([("a", 1), ("b", 4), ("b", 5), ("a", 2)]) + >>> y = sc.parallelize([("a", 3), ("c", None)]) + >>> sorted(x.subtractByKey(y).collect()) + [('b', 4), ('b', 5)] + """ + filter_func = lambda tpl: len(tpl[1][0]) > 0 and len(tpl[1][1]) == 0 + map_func = lambda tpl: [(tpl[0], val) for val in tpl[1][0]] + return self.cogroup(other, numPartitions).filter(filter_func).flatMap(map_func) + + def subtract(self, other, numPartitions=None): + """ + Return each value in C{self} that is not contained in C{other}. + + >>> x = sc.parallelize([("a", 1), ("b", 4), ("b", 5), ("a", 3)]) + >>> y = sc.parallelize([("a", 3), ("c", None)]) + >>> sorted(x.subtract(y).collect()) + [('a', 1), ('b', 4), ('b', 5)] + """ + rdd = other.map(lambda x: (x, True)) # note: here 'True' is just a placeholder + return self.map(lambda x: (x, True)).subtractByKey(rdd).map(lambda tpl: tpl[0]) # note: here 'True' is just a placeholder + + def keyBy(self, f): + """ + Creates tuples of the elements in this RDD by applying C{f}. + + >>> x = sc.parallelize(range(0,3)).keyBy(lambda x: x*x) + >>> y = sc.parallelize(zip(range(0,5), range(0,5))) + >>> sorted(x.cogroup(y).collect()) + [(0, ([0], [0])), (1, ([1], [1])), (2, ([], [2])), (3, ([], [3])), (4, ([2], [4]))] + """ + return self.map(lambda x: (f(x), x)) + # TODO: `lookup` is disabled because we can't make direct comparisons based # on the key; we need to compare the hash of the key to the hash of the # keys in the pairs. This could be an expensive operation, since those |