title: Pandas filter on categorical intervals
body: <p>I create a dataframe and categorize one column as intervals :</p>
  
  <pre><code>df_test = pd.DataFrame({'col': [0,1,2,3,4,5,6]})
  df_test['cat']= pd.cut(df_test['col'],[-1.,0.,3.,10.])
  df_test
  
          col     cat
      0   0   (-1.0, 0.0]
      1   1   (0.0, 3.0]
      2   2   (0.0, 3.0]
      3   3   (0.0, 3.0]
      4   4   (3.0, 10.0]
      5   5   (3.0, 10.0]
      6   6   (3.0, 10.0]
  </code></pre>
  
  <p>Now I want to filter this dataframe using the cat column :</p>
  
  <pre><code>df_test[df_test['cat'] == pd.Interval(left=1., right=2.)]
  
      col     cat
  1   1   (0.0, 3.0]
  2   2   (0.0, 3.0]
  3   3   (0.0, 3.0]
  </code></pre>
  
  <p>How come that checking equality with (1., 2.] yields this result ? I was expecting to get an empty result as that interval doesn't exist in the dataframe.</p>
  
  <p>Am I supposed to filter using a different method ?</p>