合并生成器对象以计算 NLTK 中的频率

Question

我想计数的各种频率ngrams使用ngram和freqDist功能nltk。由于ngram函数输出是一个generator对象，我想在计算频率之前合并每个 ngram 的输出。但是，我遇到了合并各种生成器对象的问题。

我试过itertools.chain，它创建了一个itertools对象，而不是合并生成器。我终于确定了permutations，但之后解析对象似乎是多余的。

到目前为止的工作代码是：

import nltk
from nltk import word_tokenize, pos_tag
from nltk.collocations import *
from itertools import *
from nltk.util import ngrams
import re
corpus = 'testing sentences to see if if if this works'
token = word_tokenize(corpus)
unigrams = ngrams(token,1)
bigrams = ngrams(token,2)
trigrams = ngrams(token,3)


perms = list(permutations([unigrams,bigrams,trigrams]))
fdist = nltk.FreqDist(perms)
for x,y in fdist.items():
    for k in x:
        for v in k:
            words = '_'.join(v)
            print words, y

正如您在结果中看到的那样，freq dist 没有正确计算来自单个生成器对象的单词，因为每个生成器对象的频率为 1。是否有更 Pythonic 的方法来正确执行此操作？

Answer 1

使用everygrams，它返回给定范围 n 的所有 n-gram。

>>> from nltk import everygrams
>>> from nltk import FreqDist
>>> corpus = 'testing sentences to see if if if this works'
>>> everygrams(corpus.split(), 1, 3)
<generator object everygrams at 0x7f4e272e9730>
>>> list(everygrams(corpus.split(), 1, 3))
[('testing',), ('sentences',), ('to',), ('see',), ('if',), ('if',), ('if',), ('this',), ('works',), ('testing', 'sentences'), ('sentences', 'to'), ('to', 'see'), ('see', 'if'), ('if', 'if'), ('if', 'if'), ('if', 'this'), ('this', 'works'), ('testing', 'sentences', 'to'), ('sentences', 'to', 'see'), ('to', 'see', 'if'), ('see', 'if', 'if'), ('if', 'if', 'if'), ('if', 'if', 'this'), ('if', 'this', 'works')]

结合 ngrams 的不同顺序的计数：

>>> from nltk import everygrams
>>> from nltk import FreqDist
>>> corpus = 'testing sentences to see if if if this works'.split()
>>> fd = FreqDist(everygrams(corpus, 1, 3))
>>> fd
FreqDist({('if',): 3, ('if', 'if'): 2, ('to', 'see'): 1, ('sentences', 'to', 'see'): 1, ('if', 'this'): 1, ('to', 'see', 'if'): 1, ('works',): 1, ('testing', 'sentences', 'to'): 1, ('sentences', 'to'): 1, ('sentences',): 1, ...})

或者，FreqDist本质上是一个collections.Counter子类，因此您可以将计数器组合如下：

>>> from collections import Counter
>>> x = Counter([1,2,3,4,4,5,5,5])
>>> y = Counter([1,1,1,2,2])
>>> x + y
Counter({1: 4, 2: 3, 5: 3, 4: 2, 3: 1})
>>> x

>>> from nltk import FreqDist
>>> FreqDist(['a', 'a', 'b'])
FreqDist({'a': 2, 'b': 1})
>>> a = FreqDist(['a', 'a', 'b'])
>>> b = FreqDist(['b', 'b', 'c', 'd', 'e'])
>>> a + b
FreqDist({'b': 3, 'a': 2, 'c': 1, 'e': 1, 'd': 1})