title: Indexing with multiindex dataframe in pandas
body: <p>Consider the following example data:</p>
  
  <pre><code>data = {"Taxon": ["Firmicutes"]*5,
          "Patient": range(5),
          "Tissue": np.random.randint(0, 1000, size=5),
          "Stool": np.random.randint(0, 1000, size=5)}
  
  df = pd.DataFrame(data).set_index(["Taxon", "Patient"])
  print(df)
  
                      Stool  Tissue
  Taxon      Patient               
  Firmicutes 0          740     389
             1          786     815
             2          178     265
             3          841     484
             4          211     534
  </code></pre>
  
  <p>So, How can I query the dataframe only with the second level index <code>Patient</code> only? For example, I'd like to know all the data with respect to <code>Patient 2</code>.</p>
  
  <p>I've tried <code>data[data.index.get_level_values(1)==2]</code>, and it worked fine. But is there any way to achieve the same with one these (<code>loc</code>,<code>iloc</code> or <code>ix</code>) indexing methods?</p>