如何无法索引到reduce的值列表? [英] How can I cannot index into the values list of reduce?

问题描述

我正在通过Python mrjob模块在Map Reduce作业中使用映射器内合并.因为我写了一个mapper_final函数，该函数会发出一对，所以我确定只有一个键值对会发给我的精简器.

I am using in-mapper combining in a Map Reduce job via the Python mrjob module. Because I wrote a mapper_final function that emits a single pair, I am sure that only a single key-value pair is emitted to my reducers.

但是，我的reduce函数出错了

However, my reduce function is erring:

  def reducer(self, key, occurrences):
    '''
    Calculates the final value.
    '''
    yield 'Final Value: ', occurrences[0] / 2

读取错误

File "calculateFinalValue.py", line 354, in reducer
    yield 'Final Value: ', occurrences[0] / 2
TypeError: 'generator' object has no attribute '__getitem__'

为什么我不能索引到occurrences?该列表中应该只有一对，对吧?

Why can I not index into occurrences? There should only be a single pair in that list, right?

推荐答案

occurrences不是list，而是 generator .如果需要list，则需要将生成器结果组合到一个列表中.像这样:

occurrences is not a list, it is a generator. If you want a list, you need to assemble the generator results into a list. Something like:

list_occurrences = [ occ for occ in occurrences ]

或

list_occurrences = list(occurrences)

yield 'Final Value: ', list_occurrences[0] / 2

或者您可以通过occurrences.next()获取出现的第一个值:

Or you can get the first value of occurrences with occurrences.next():

yield 'Final Value: ', occurrences.next() / 2

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