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basic.py
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basic.py
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from __future__ import division
from collections import Counter
from nltk.corpus import brown
from nltk.util import ngrams
from nltk.tokenize import sent_tokenize, word_tokenize
from nltk.tokenize import RegexpTokenizer
#Code to read the sentence from the file
file = open('test.txt','r')
sentence = file.read();
sentence_broke = sent_tokenize(sentence)
#Thoe following code snippets work in the following fashion
#Line 1 refers to an array that stores the count of the n-grams
#Line 2 refers to the brown corpus broken into n-grams
#Line 3 calculates the frequency of the ngrams in corpus
#Code snippet that works upon the unigrams list
unigrams = ngrams(brown.words(),1)
unigrams_freq = Counter(unigrams);
#Code snippet that works upon the bigrams list
bigrams = ngrams(brown.words(),2)
bigrams_freq = Counter(bigrams);
#Code snippet that works upon the trigrams list
trigrams = ngrams(brown.words(),3)
trigrams_freq = Counter(trigrams);
len_corpus = brown.words().__len__()
for sentence in sentence_broke:
tokened = RegexpTokenizer(r'\w+')
tokened = tokened.tokenize(sentence)
unigram_set = ngrams(tokened,1)
bigram_set = ngrams(tokened,2)
trigram_set = ngrams(tokened,3)
w2 = "*"
w1 = "*"
uni_q = []
bi_q = []
tri_q = []
bi_q.append(1.0)
tri_q.append(1.0)
tri_q.append(1.0)
ans = 0.0
q_trigram_count = 1.0
lambda1 = 1.0/3.0
lambda2 = 1.0/3.0
lambda3 = 1.0/3.0
for words in unigram_set:
uni_q.append(unigrams_freq[words])
for words in bigram_set:
bi_q.append(bigrams_freq[words])
for words in trigram_set:
tri_q.append(trigrams_freq[words])
for i in range(2,tokened.__len__()):
ans = 0.0 if bi_q[i-1] == 0 else float(tri_q[i])/float(bi_q[i-1])
ans += 0.0 if uni_q[i-1] == 0 else float(bi_q[i])/float(uni_q[i-1])
ans += float(uni_q[i])/float(len_corpus)
ans = ans/3;
q_trigram_count *= ans
#q_trigram_count now has the product of all the probabilities in it
print(sentence,q_trigram_count)