[英]Hadoop MapReduce job on file containing HTML tags
我有一堆大型HTML文件,我想在它们上运行Hadoop MapReduce作业以查找最常用的单词。 我用Python编写了mapper和reducer,并使用Hadoop流来运行它们。
这是我的映射器:
#!/usr/bin/env python
import sys
import re
import string
def remove_html_tags(in_text):
'''
Remove any HTML tags that are found.
'''
global flag
in_text=in_text.lstrip()
in_text=in_text.rstrip()
in_text=in_text+"\n"
if flag==True:
in_text="<"+in_text
flag=False
if re.search('^<',in_text)!=None and re.search('(>\n+)$', in_text)==None:
in_text=in_text+">"
flag=True
p = re.compile(r'<[^<]*?>')
in_text=p.sub('', in_text)
return in_text
# input comes from STDIN (standard input)
global flag
flag=False
for line in sys.stdin:
# remove leading and trailing whitespace, set to lowercase and remove HTMl tags
line = line.strip().lower()
line = remove_html_tags(line)
# split the line into words
words = line.split()
# increase counters
for word in words:
# write the results to STDOUT (standard output);
# what we output here will be the input for the
# Reduce step, i.e. the input for reducer.py
#
# tab-delimited; the trivial word count is 1
if word =='': continue
for c in string.punctuation:
word= word.replace(c,'')
print '%s\t%s' % (word, 1)
这是我的减速器:
#!/usr/bin/env python
from operator import itemgetter
import sys
# maps words to their counts
word2count = {}
# input comes from STDIN
for line in sys.stdin:
# remove leading and trailing whitespace
line = line.strip()
# parse the input we got from mapper.py
word, count = line.split('\t', 1)
# convert count (currently a string) to int
try:
count = int(count)
word2count[word] = word2count.get(word, 0) + count
except ValueError:
pass
sorted_word2count = sorted(word2count.iteritems(),
key=lambda(k,v):(v,k),reverse=True)
# write the results to STDOUT (standard output)
for word, count in sorted_word2count:
print '%s\t%s'% (word, count)
每当我通过管道传送一个小的示例小字符串(例如“ hello world hello hello world ...”)时,我都会获得适当的排名列表输出。 但是,当我尝试使用一个小的HTML文件并尝试使用cat将HTML管道传输到我的映射器时,出现以下错误(input2包含一些HTML代码):
rohanbk@hadoop:~$ cat input2 | /home/rohanbk/mapper.py | sort | /home/rohanbk/reducer.py
Traceback (most recent call last):
File "/home/rohanbk/reducer.py", line 15, in <module>
word, count = line.split('\t', 1)
ValueError: need more than 1 value to unpack
谁能解释我为什么得到这个? 另外,调试MapReduce作业程序的好方法是什么?
您甚至可以重现该错误:
echo "hello - world" | ./mapper.py | sort | ./reducer.py
问题在这里:
if word =='': continue
for c in string.punctuation:
word= word.replace(c,'')
如果word
是单个标点符号(与上述输入一样)(拆分后),那么它将转换为空字符串。 因此,只需将替换后的空字符串检查移至即可。
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