title: Merging dataframes on index with pandas
body: <p>I have two dataframes and each one has two index columns. I would like to merge them. For example, the first dataframe is the following:</p>
  
  <pre><code>                   V1
  
  A      1/1/2012    12
         2/1/2012    14
  B      1/1/2012    15
         2/1/2012    8
  C      1/1/2012    17
         2/1/2012    9
  </code></pre>
  
  <p>The second dataframe is the following:</p>
  
  <pre><code>                   V2
  
  A      1/1/2012    15
         3/1/2012    21             
  B      1/1/2012    24
         2/1/2012    9
  D      1/1/2012    7
         2/1/2012    16
  </code></pre>
  
  <p>and as result I would like to get the following:</p>
  
  <pre><code>                   V1   V2
  
  A      1/1/2012    12   15
         2/1/2012    14   N/A
         3/1/2012    N/A  21           
  B      1/1/2012    15   24
         2/1/2012    8    9
  C      1/1/2012    7    N/A
         2/1/2012    16   N/A
  D      1/1/2012    N/A  7
         2/1/2012    N/A  16
  </code></pre>
  
  <p>I have tried a few versions using the <code>pd.merge</code> and <code>.join</code> methods, but nothing seems to work. Do you have any suggestions?</p>