title: transform scipy sparse csr to pandas?
body: <p>I have used the</p>
  
  <pre><code>sklearn.preprocessing.OneHotEncoder
  </code></pre>
  
  <p>to transform some data the output is <code>scipy.sparse.csr.csr_matrix</code>
  how can I merge it back into my original dataframe along with the other columns?</p>
  
  <p>I tried to use <code>pd.concat</code> but I get </p>
  
  <pre><code>TypeError: cannot concatenate a non-NDFrame object
  </code></pre>
  
  <p>Thanks</p>