title: extract pos_tag_sents from pandas series
body: <p>following the advice from the thread <a href="https://stackoverflow.com/questions/41674573/how-to-apply-pos-tag-sents-to-pandas-dataframe-efficiently">How to apply pos_tag_sents() to pandas dataframe efficiently</a> I run the code to identify different pos for the text in one of my variables. </p>
  
  <p>Now that I managed to create the column of interest - sub['POS'] - how do I extract my relevant information - all the NN - and create a column for each of them?</p>
  
  <pre><code>print(sub['POS'])
  
  5     [(e-mail, JJ), (new, JJ), (delhi, NN), ((, (),...
  4     [(bangladesh, JJ), (garment, NN), (unions, NNS...
  41    [(listen, VB), (blaze, NN), (wrecks, NNS), (te...
  10    [(11:49, CD), (am, VBP), (,, ,), (september, V...
  17    [(listen, JJ), (two, CD), (events, NNS), (plan...
  </code></pre>
  
  <p>as an output, I would like a new column (here as 'NN'), that contains all the NN for each row. </p>
  
  <pre><code>df = pd.DataFrame(["delhi", 
                     "garment" , 
                     "blaze", 
                     NaN], columns=['NN'])
  </code></pre>