title: Getting Ngram frequency from a a large corpus of txt. files
body: <p>I need to develop a code for counting Ngram (1,2,3,4,5,6) frequencies in a large txt corpus using NLTK. I have two problems: 
  1: I have the following code to import the files as bulk: </p>
  
  <pre><code>from nltk.corpus import PlaintextCorpusReader
  
  Corpus_root = 'C/x/x/Myfolder'
  files = PlaintextCorpusReader(corpus_root, '.*')
  files.fileids()
  </code></pre>
  
  <p>gives me an output of all my files read into NLTK. </p>
  
  <p>My first problem is how to connect the corpus reader to the upcoming code to count the ngrams? </p>
  
  <p>My problem in the next step is what module of code should I use to count bigram, trigram and four &amp; five gram and their frequencies which is efficient and fast? </p>
  
  <p>I have 300 txt files and want to use them to get ngram frequency.</p>