理解MapReduce

Posted 2020-11-04 097黄大贞

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用Python编写WordCount程序任务

程序	WordCount
输入	一个包含大量单词的文本文件
输出	文件中每个单词及其出现次数（频数），并按照单词字母顺序排序，每个单词和其频数占一行，单词和频数之间有间隔

编写map函数，reduce函数

# map函数
import sys
for i in stdin:
     i = i.strip()
     words = i.split()
     for word in words:
         print \'%s\\t%s\' % (word,1)

#reduce函数
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 word == current_word: 
    print "%s\\t%s" % (current_word, current_count)

将其权限作出相应修改

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

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

本机上测试运行代码

echo "foo foo quux labs foo bar quux" | /home/hadoop/wc/mapper.py
echo "foo foo quux labs foo bar quux" | /home/hadoop/wc/mapper.py | sort -k1,1 | /home/hadoop/wc/reducer.p