python - Generating Ngrams (Unigrams,Bigrams etc) from a large corpus of .txt files and their Frequency

Question

I need to write a program in NLTK that breaks a corpus (a large collection of txt files) into unigrams, bigrams, trigrams, fourgrams and fivegrams. I have already written code to input my files into the program.

The input is 300 .txt files written in English and I want the output in form of Ngrams and specially the frequency count.

I know that NLTK has Bigram and Trigram modules : http://www.nltk.org/_modules/nltk/model/ngram.html

but I am not that advanced to enter them into my program.

input: txt files NOT single sentences

output example:

Bigram [('Hi', 'How'), ('How', 'are'), ('are', 'you'), ('you', '?'), ('?', 'i'), ('i', 'am'), ('am', 'fine'), ('fine', 'and'), ('and', 'you')] 

Trigram: [('Hi', 'How', 'are'), ('How', 'are', 'you'), ('are', 'you', '?'), ('you', '?', 'i'), ('?', 'i', 'am'), ('i', 'am', 'fine'), ('am', 'fine', 'and'), ('fine', 'and', 'you')]

My code up to now is:

from nltk.corpus import PlaintextCorpusReader
corpus = 'C:/Users/jack3/My folder'
files = PlaintextCorpusReader(corpus, '.*')
ngrams=2

def generate(file, ngrams):
    for gram in range(0, ngrams):
    print((file[0:-4]+"_"+str(ngrams)+"_grams.txt").replace("/","_"))


for file in files.fileids():
generate(file, ngrams)

Any help what should be done next?

Answer 1

Just use ntlk.ngrams.

import nltk
from nltk import word_tokenize
from nltk.util import ngrams
from collections import Counter

text = "I need to write a program in NLTK that breaks a corpus (a large collection of 
txt files) into unigrams, bigrams, trigrams, fourgrams and fivegrams. 
I need to write a program in NLTK that breaks a corpus"
token = nltk.word_tokenize(text)
bigrams = ngrams(token,2)
trigrams = ngrams(token,3)
fourgrams = ngrams(token,4)
fivegrams = ngrams(token,5)

print Counter(bigrams)

Counter({('program', 'in'): 2, ('NLTK', 'that'): 2, ('that', 'breaks'): 2,
 ('write', 'a'): 2, ('breaks', 'a'): 2, ('to', 'write'): 2, ('I', 'need'): 2,
 ('a', 'corpus'): 2, ('need', 'to'): 2, ('a', 'program'): 2, ('in', 'NLTK'): 2,
 ('and', 'fivegrams'): 1, ('corpus', '('): 1, ('txt', 'files'): 1, ('unigrams', 
','): 1, (',', 'trigrams'): 1, ('into', 'unigrams'): 1, ('trigrams', ','): 1,
 (',', 'bigrams'): 1, ('large', 'collection'): 1, ('bigrams', ','): 1, ('of',
 'txt'): 1, (')', 'into'): 1, ('fourgrams', 'and'): 1, ('fivegrams', '.'): 1,
 ('(', 'a'): 1, (',', 'fourgrams'): 1, ('a', 'large'): 1, ('.', 'I'): 1, 
('collection', 'of'): 1, ('files', ')'): 1})

UPDATE (with pure python):

import os

corpus = []
path = '.'
for i in os.walk(path).next()[2]:
    if i.endswith('.txt'):
        f = open(os.path.join(path,i))
        corpus.append(f.read())
frequencies = Counter([])
for text in corpus:
    token = nltk.word_tokenize(text)
    bigrams = ngrams(token, 2)
    frequencies += Counter(bigrams)