title: removing bigrams that contain common stopwords
body: <p>I have a function as below. It returns all bigrams and trigram in a sentence. I would like to keep only bigrams and trigrams that dont contain any stopwords. How could I use <code>from nltk.copus import stopwords</code> to do the same? </p>
  
  <p>I know how to remove remove stopwords before creating bigrams and trigrams. But I would like to remove stopwords after creating bigrams and trigrams. </p>
  
  <pre><code>from nltk import everygrams
  from nltk.copus import stopwords
  
  
  def clean_text_function2(text):
      t = text #contractions.fix(text)
      t= t.lower().split()#lower case
      t = [(re.sub(r'[^a-z ]', '', ch)) for ch in t]#remove everything other than a-z
      #t=[word for word in t if word not in stopword]#removing stop words
      t= [wordnet_lemmatizer.lemmatize(word) for word in t]
      t=[snowball_stemmer.stem(word) for word in t]
      t=(' ').join(t)
      t=list(everygrams(t.split(), 2, 3))
      return t
  
  
  
  
  
  
  print (clean_text_function2("i love when it rains a lot and brings temperature down"))
  
  [('i', 'love'), ('love', 'when'), ('when', 'it'), ('it', 'rain'), ('rain', 'a'), ('a', 'lot'), ('lot', 'and'), ('and', 'bring'), ('bring', 'temperatur'), ('temperatur', 'down'), ('i', 'love', 'when'), ('love', 'when', 'it'), ('when', 'it', 'rain'), ('it', 'rain', 'a'), ('rain', 'a', 'lot'), ('a', 'lot', 'and'), ('lot', 'and', 'bring'), ('and', 'bring', 'temperatur'), ('bring', 'temperatur', 'down')]
  </code></pre>