title: Convert Pandas SparseDataframe to Scipy sparse csc_matrix
body: <p>I want to convert a pandas <code>SparseDataFrame</code> to a <code>scipy.sparse.csc_matrix</code>. But I don't want to convert it back to a dense matrix first.</p>
  
  <p>Right now I have something like the below.</p>
  
  <pre><code>df = pd.get_dummies(df, sparse=True)
  </code></pre>
  
  <p>Basically what I need is to further get a <code>scipy.sparse.csc_matrix</code> from <code>df</code>. Is there a way to do it?</p>