docs: def to_ngrams(self, terms):
          ''' Converts terms to all possibe ngrams 
              terms: list of terms
          '''
          if len(terms) <= self.n:
              return terms
          if self.n == 1:
              n_grams = [[term] for term in terms]
          else:
              n_grams = []
              for i in range(0,len(terms)-self.n+1):
                  n_grams.append(terms[i:i+self.n])
          return n_grams