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以下是 python 中的 map-reduce 脚本，用于查找特定列的计数。输入文件如下：

 301838690844557314|#awkwarddate first date at     quiznoes|334910568|gabriellarichh|20130213|awkwarddate|Point|40.456664|-74.265167
 301838679280861185|RT @jimmyfallon: Ended my very first date by saying, "Take it easy." And  then my dad drove me home.  #awkwarddate|618516844|heyitsbrooke456|20130213|awkwarddate|NULL|NULL|NULL
 301838678026768384|RT @jimmyfallon: Hashtag game! Tweet out a funny, weird, or embarrassing story about a date you've been on and tag w/ #awkwarddate. Could be on our show!|116973704|VegasPhotog|20130213|awkwarddate|NULL|NULL|NULL

map reduce脚本是：map代码是：

import sys

def read_input(file):
    for line in file:
        # split the line into words
        yield line.split('|')

def main(separator='|'):
    # input comes from STDIN (standard input)
    data = read_input(sys.stdin)
    for words in data:
        # 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 len(words)==9:
            for word[5] in words:
                print '%s%s%d' % (word[5], separator, 1)

if __name__ == "__main__":
    main()

减少代码是：

from itertools import groupby
from operator import itemgetter
import sys

def read_mapper_output(file, separator='|'):
    for line in file:
        yield line.rstrip().split(separator, 1)

def main(separator='|'):
    # input comes from STDIN (standard input)
    data = read_mapper_output(sys.stdin, separator=separator)
    # groupby groups multiple word-count pairs by word,
    # and creates an iterator that returns consecutive keys and their group:
    #   current_word - string containing a word (the key)
    #   group - iterator yielding all ["<current_word>", "<count>"] items
    for current_word, group in groupby(data, itemgetter(0)):
        try:
            total_count = sum(int(count) for current_word, count in group)
            print "%s%s%d" % (current_word, separator, total_count)
        except ValueError:
            # count was not a number, so silently discard this item
            pass

if __name__ == "__main__":
    main()

当我在 hadoop 中运行上述脚本时，出现以下错误：

failed Map Tasks exceeded allowed limit. FailedCount: 1. LastFailedTask: task_201302281754_0001_m_000000

我想获得第 6 列的计数（awkwarddate）任何帮助将不胜感激。提前致谢

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1 回答 1

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让我们进一步分解一下，因为您想计算每行的第 6 列。

def to_std_out(line, sep='|'):
    words = line.split(sep)

    print '%s%s%d' % (words[5], sep, 1)

现在在您的脚本入口点（在您的案例中表示为main()函数），逻辑可能是：

def main(sep='|'):
    # read in stdin line by line, usually you might need an indefinite loop
    # for the sake of simplicity, I'll be using while 1
    while 1:
        lines = sys.stdin.readlines()
        for line in lines:
            to_std_out(line, sep)

希望这就是你要找的:)

于 2013-02-28T15:15:57.770 回答