title: Best solution for selecting the columns that contain at least one True value in a pandas DataFrame
body: <pre><code>In [4]: df = pd.DataFrame({'a': [True, False, True], 'b': [False, False, False], 
     ...: 'c': [False, False, False], 'd': [False, True, False], 
     ...: 'e': [False, False, False]})                                                                                                                                                                                                                                              
  
  
  In [5]: df                                                                                                                                                                                                                                                                        
  Out[5]: 
         a      b      c      d      e
  0   True  False  False  False  False
  1  False  False  False   True  False
  2   True  False  False  False  False
  
  In [6]: df[df.any()[df.any()].index]                                                                                                                                                                                                                                              
  Out[6]: 
         a      d
  0   True  False
  1  False   True
  2   True  False
  </code></pre>
  <p>The code under [6] does what I want. My question, however, is: is there a better solution? That is, more concise and/or more elegant.</p>