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	%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('	',1)
     try:
          count=int(count)
     except ValueError:
          continue
     if current_word==word:
          current_count+=count
     else:
          if current_word:
              print '%s	%s' % (current_word,current_count)
          current_count=count
          current_word=word
if current_word==word:
     print '%s	%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

E.查看运行结果

 2.

A.气象数据集下载地址为：ftp://ftp.ncdc.noaa.gov/pub/data/noaa

按学号后三位下载不同年份月份的数据（例如201506110136号同学，就下载2013年以6开头的数据，看具体数据情况稍有变通）

mkdir qx
cd qx
wget -D --accept-regex=REGEX -p data -r -c ftp://ftp.ncdc.noaa.gov/pub/data/noaa/2009/8*

B.解压数据集，并保存在文本文件中

C.对气象数据格式进行解析

cd qx/data/ftp.ncdc.noaa.gov/pub/data/noaa/2009
sudo zcat 8*.gz >qxdata.txt
head qxdata.txt

编写map函数，reduce函数

#！/usr/bin/env python
import sys
for i in sys.stdin:
     i = i.strip()
     d = i[15:23]
     t = i[87:92]
     print '%s	%s' % (d,t)

#!/usr/bin/env python
from operator import itemggetter
import sys

current_word = None
current_count = 0
word = None

for i in sys.stdin:
     i = i.strip()
     word,count = i.split('	', 1)
     try:
          count = int(count)
     except ValueError:
          continue

     if current_word == word:
         if current_count > count:
              current_count = count
     else:
         if current_word:
             print '%s	%s' % (current_word, current_count)
         current_count = count
         current_word = word

if current_word == word:
     print '%s	%s' % (current_word, current_count)

将其权限作出相应修改

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

本机上测试运行代码

放到HDFS上运行

将之前爬取的文本文件上传到hdfs上

用Hadoop Streaming命令提交任务

start-dfs.sh
jps
hdfs dfs -put ./*.txt /user/hadoop/input
hdfs dfs -ls input

查看运行结果