Python结合Shell/Hadoop实现MapReduce
基本流程为：cat data | map | sort | reduce
cat devProbe | ./mapper.py | sort| ./reducer.py
echo "foo foo quux labs foo bar quux" | ./mapper.py | sort -k1,1 | ./reducer.py
# -k, -key=POS1[,POS2] 键以pos1开始，以pos2结束
如不执行下述命令，可以再py文件前加上python调用
chmod +x mapper.py
chmod +x reducer.py
对于分布式环境下，可以使用以下命令：
hadoop jar //hadoop/tools/lib/hadoop-streaming-2.6.0-cdh5.4.4.jar \
-file mapper.py -mapper mapper.py \
-file reducer.py -reducer reducer.py \
-input -output
mapper.py
#!/usr/bin/python
#
-*- coding: UTF-8 -*-
__author__ = 'Manhua'
import sys
for line in sys.stdin:
line = line.strip()
item = line.split('`')
print "%s\t%s" % (item+'`'+item, 1)
reducer.py
#!/usr/bin/python
#
-*- coding: UTF-8 -*-
__author__ = 'Manhua'
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:#count如果不是数字的话，直接忽略掉
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:#不要忘记最后的输出
print "%s\t%s" % (current_word, current_count)
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