title: Find the most frequent word pair from a list of messages in python
body: <p>i have a list of 100 messages. And i am able to find the most frequent words used in the list of messages.
  But i want to find the pair of words which occur most frequently.
  For example, key and board are being shown as most frequent words. But i need to find the number of occurrences where 'key board' are used as a pair in NLTK.
  Here abstracts are the list of sentences and abstract words are list of words.</p>
  
  <pre><code>abstracts = [preprocessing(document) for document in abstracts]
  
  abstract_words = " ".join(abstracts)
  abstract_words = abstract_words.split()
  
  def plot_word_frequency(words, top_n=10):
      word_freq = FreqDist(words)
      labels = [element[0] for element in word_freq.most_common(top_n)]
      counts = [element[1] for element in word_freq.most_common(top_n)]
      plot = sns.barplot(labels, counts)
      return plot
  
  plot_word_frequency(abstract_words, 10)
  </code></pre>
  
  <p>Here i am able to plot the individual top 10 words. But need to plot combination of words which are most frequent.                                                        </p>