Streaming执行Python版WordCount
一：先写map类import sys
for line in sys.stdin:
line = line.strip( )
words = line.split( )
for word in words:
print('%s\t%s' % (word, 1))
二：写reduce类
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))
三：利用hadoop Streaming执行Python的内容。
hadoop jar /home/hadoop/hadoop-2.6.0-cdh5.5.2/share/hadoop/tools/lib/hadoop-streaming-2.6.0-cdh5.5.2.jar-input /user/hadoop/aa.txt -output /user/hadoop/python_output -mapper "python mapper.py" -reducer "python reducer.py" -file mapper.py -file reducer.py
说明：
输入和输出路径，本身就是hdfs上的，不需要特殊指定hdfs。
不加黄色部分的引号的话，会报错误：
Error: java.lang.RuntimeException: PipeMapRed.waitOutputThreads(): subprocess failed with code 2
不加粉色部分的内容的话，会报错误：
Error: java.lang.RuntimeException: Error in configuring object
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