我如何将双字母对的频率除以会标字？

Question

below is my code.

from __future__ import division
import nltk
import re

f = open('C:/Python27/brown_A1_half.txt', 'rU')
w = open('C:/Python27/brown_A1_half_Out.txt', 'w')

#to read whole file using read()

filecontents = f.read()
from nltk.tokenize import sent_tokenize
sent_tokenize_list = sent_tokenize(filecontents)

for sentence in sent_tokenize_list:
    sentence = "Start " + sentence + " End"
    tokens = sentence.split()
    bigrams = (tuple(nltk.bigrams(tokens)))
    bigrams_frequency = nltk.FreqDist(bigrams)
    for k,v in bigrams_frequency.items():
        print k, v 

then the printing result is "(bigrams), its frequency ". here, what I want is for each bigram pair, divide the bigram frequency by the first appearing unigram word frequency. (for example, if there is a bigram ('red', 'apple') and its frequency is "3", then I want to divide it by the frequency of 'red'). This is for obtaining the MLE prob, that is "MLE prob = Counting of (w1, w2) / Counting of (w1)" . help me plz...

Answer 1

You can add the following in the for loop (after print k, v):

number_unigrams = tokens.count(k[0])
prob = v / number_unigrams

That should give you the MLE prob for each bigram.