理解MapReduce

1.

A.编写map函数，reduce函数

#！/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)

#！/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)

B.将其权限作出相应修改

chmod a+x /home/hadoop/wc/mapper.py

chmod a+x /home/hadoop/wc/reducer.py

C.本机上测试运行代码

D.放到HDFS上运行

         a.将之前爬取的文本文件上传到hdfs上

         b.用Hadoop Streaming命令提交任务