python基于Hadoop Streaming实现简单的WordCount

1. Eclipse下配置python插件PyDev

参考：http://blog.chinaunix.net/uid-11121450-id-1476897.html

2. Hadoop Streaming编程

Hadoop Streaming是利用“标准输入”和“标准输出”与我们编写的Map和Reduce进行数据的交换。
那么，任何能够使用“标准输入”和“标准输出”的编程语言都应该可以用来编写MapReduce程序。

 

3. Python实现简单的Word Count程序

需要注意python中对分隔符的要求比较严格，尽量不要混用tab和空格，很容易导致编译失败

mapper.py

#!/usr/bin/python
import sys 
for line in sys.stdin:
 #去除字符串两边的空格 
 line = line.strip() 
 #按照空格去划分单词
 words = line.split()
  for word in words:
   print '%s %s' % (word, 1)

 

reducer.py

#!/usr/bin/python 
from operator import itemgetter
import sys 
word2count = {} 
for line in sys.stdin:
   line = line.strip() 
   word, count = line.split(' ', 1)   
   try:
    count = int(count)
    word2count[word] = word2count.get(word, 0) + count
   except ValueError:      
    pass 
   sorted_word2count = sorted(word2count.items(), key=itemgetter(0))
   for word, count in sorted_word2count:
    print '%s %s'% (word, count)

 

 

4. 在hadoop上运行python脚本

#在Hadoop Home路径下运行以下命令
 bin/hadoop jar contrib/streaming/hadoop-streaming-1.0.0.jar -mapper /usr/local/mapper.py -reducer /usr/local/reducer.py -input /test.txt -output /result