pyspark.RDD.reduceByKey¶
-
RDD.reduceByKey(func, numPartitions=None, partitionFunc=<function portable_hash>)[source]¶ Merge the values for each key using an associative and commutative reduce function.
This will also perform the merging locally on each mapper before sending results to a reducer, similarly to a “combiner” in MapReduce.
Output will be partitioned with numPartitions partitions, or the default parallelism level if numPartitions is not specified. Default partitioner is hash-partition.
Examples
>>> from operator import add >>> rdd = sc.parallelize([("a", 1), ("b", 1), ("a", 1)]) >>> sorted(rdd.reduceByKey(add).collect()) [('a', 2), ('b', 1)]