[英]How to count the number of times a word sequence appears in a file, using MapReduce in Python?
考虑一个包含由空格分隔的单词的文件; 在Python中编写一个MapReduce程序,统计每个3字序列在文件中出现的次数。
例如,考虑以下文件:
one two three seven one two three
three seven one
seven one two
每个 3 字序列在该文件中出现的次数为:
"three seven one" 2
"four seven one two" 1
"one two three" 2
"seven one two" 2
"two three seven" 1
代码格式:
from mrjob.job import MRJob
class MR3Nums(MRJob):
def mapper(self,_, line):
pass
def reducer(self,key, values):
pass
if __name__ == "__main__":
MR3Nums.run()
映射器应用于每一行,并且应该计算每个 3-word 序列,即产生 3-word 序列以及计数为 1。
使用key
和values
调用 reducer,其中key
是一个 3 字序列,而values
是一个计数列表(这将是一个 1 的列表)。 reducer 可以简单地返回一个 3 词序列的元组和出现的总次数,后者通过 sum 获得。
class MR3Nums(MRJob):
def mapper(self, _, line):
sequence_length = 3
words = line.strip().split()
for i in range(len(words) - sequence_length + 1):
yield " ".join(words[i:(i+sequence_length)]), 1
def reducer(self, key, values):
yield key, sum(values)
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