diff --git a/python/pyspark/rdd.py b/python/pyspark/rdd.py index 0f28dbd6fcc09ae8f174bb5a7ed469e9e1809b1e..6d549b40e5698246766c81d5159353adae137678 100644 --- a/python/pyspark/rdd.py +++ b/python/pyspark/rdd.py @@ -29,6 +29,7 @@ from subprocess import Popen, PIPE from tempfile import NamedTemporaryFile from threading import Thread import warnings +from heapq import heappush, heappop, heappushpop from pyspark.serializers import NoOpSerializer, CartesianDeserializer, \ BatchedSerializer, CloudPickleSerializer, PairDeserializer, pack_long @@ -660,6 +661,30 @@ class RDD(object): m1[k] += v return m1 return self.mapPartitions(countPartition).reduce(mergeMaps) + + def top(self, num): + """ + Get the top N elements from a RDD. + + Note: It returns the list sorted in ascending order. + >>> sc.parallelize([10, 4, 2, 12, 3]).top(1) + [12] + >>> sc.parallelize([2, 3, 4, 5, 6]).cache().top(2) + [5, 6] + """ + def topIterator(iterator): + q = [] + for k in iterator: + if len(q) < num: + heappush(q, k) + else: + heappushpop(q, k) + yield q + + def merge(a, b): + return next(topIterator(a + b)) + + return sorted(self.mapPartitions(topIterator).reduce(merge)) def take(self, num): """