This topic describes how to use Python to create a Hadoop streaming job.
Use Python to create a Hadoop streaming job
The mapper code is as follows:
#! /usr/bin/env python import sys for line in sys.stdin: line = line.strip() words = line.split() for word in words: print '%s\t%s' % (word, 1)
The reducer code is as follows:
#! /usr/bin/env python from operator import itemgetter import sys current_word = None current_count = 0 word = None for line in sys.stdin: line = line.strip() word, count = line.split('\t', 1) try: count = int(count) except ValueError: continue if current_word == word: current_count += count else: if current_word: print '%s\t%s' % (current_word, current_count) current_count = count current_word = word if current_word == word: print '%s\t%s' % (current_word, current_count)
Suppose that the mapper code is saved as /home/hadoop/mapper.py and the reducer code is saved as /home/hadoop/reducer.py, and that the paths for input and output are /tmp/input and /tmp/output in the HDFS file system respectively. Submit the following Hadoop command in the E-MapReduce cluster.
hadoop jar /usr/lib/hadoop-current/share/hadoop/tools/lib/hadoop-streaming-*.jar -file /home/hadoop/mapper.py -mapper mapper.py -file /home/hadoop/reducer.py -reducer reducer.py -input /tmp/hosts -output /tmp/output