title: Recover named features from L1 regularized logistic regression
body: <p>I have the following pipeline:</p>
  
  <pre><code>sg = Pipeline([('tfidf', TfidfVectorizer()),                                                                                                                                            
                 ('normalize', Normalizer()),                                                                                                                                                 
                 ('l1', LogisticRegression(penalty="l1", dual=False))])
  </code></pre>
  
  <p>and after peforming the fitting, I want to extract the tokens that correnponds
  to the non-zero weights.</p>
  
  <p>How can I do this?</p>