title: Grouping date index in pandas
body: <p>I have a dataframe looks like this:</p>
  
  <pre><code>   In [101]:
  
  import pandas as pd
  df = pd.DataFrame( {'date':['2014-06-30','2014-06-30','2014-06-29','2014-06-29','2014-06-29'], 'value':[1,2,5,5,4]})
  df.set_index('date')
  Out[101]:
           value
  date    
  2014-06-30  1
  2014-06-30  2
  2014-06-29  5
  2014-06-29  5
  2014-06-29  4
  </code></pre>
  
  <p>In here, I want to group index column based on the date value. The desired output should be like this:</p>
  
  <pre><code>df
  Out[102]:
             value
  date    
  2014-06-30  1
              2
  2014-06-29  5
              5
              4
  </code></pre>
  
  <p>So, if I use df.iloc[0] the output should be like this:</p>
  
  <pre><code>2014-06-30      1
                  2
  </code></pre>