title: Joining Pandas dataframes in Python with the same index multiple times
body: <p>I have two dataframes: </p>
  
  <pre><code>&gt;&gt;&gt;import import pandas as pd
  &gt;&gt;&gt;df1:
  
                   DD_PRICE
  DATE                         
  2013-09-19 20:55:00  3.516
  2013-09-19 20:55:00  3.516
  2013-09-19 20:55:00  3.516
  2013-09-19 20:55:00 -4.476
  
  &gt;&gt;&gt;df2:
                   CAPI_PRICE
  DATE                         
  2013-09-19 20:55:00  3.516
  2013-09-19 20:55:00  3.516
  2013-09-19 20:55:00  3.516
  2013-09-19 20:55:00 -4.476
  </code></pre>
  
  <p>Now when I run:</p>
  
  <pre><code> joint_df = df1.join((df2), how='outer')
  </code></pre>
  
  <p><code>joint_df</code> looks like this:</p>
  
  <pre><code>                  DD_PRICE  CAPI_PRICE
  DATE                                   
  2013-09-19 20:55:00  3.516  3.516
  2013-09-19 20:55:00  3.516  3.516
  2013-09-19 20:55:00  3.516  3.516
  2013-09-19 20:55:00  3.516 -4.476
  2013-09-19 20:55:00  3.516  3.516
  2013-09-19 20:55:00  3.516  3.516
  2013-09-19 20:55:00  3.516  3.516
  2013-09-19 20:55:00  3.516 -4.476
  2013-09-19 20:55:00  3.516  3.516
  2013-09-19 20:55:00  3.516  3.516
  2013-09-19 20:55:00  3.516  3.516
  2013-09-19 20:55:00  3.516 -4.476
  2013-09-19 20:55:00 -4.476  3.516
  2013-09-19 20:55:00 -4.476  3.516
  2013-09-19 20:55:00 -4.476  3.516
  2013-09-19 20:55:00 -4.476 -4.476
  </code></pre>
  
  <p>This isnt what I want... </p>
  
  <p>Ideally I want <code>joint_df</code> to look like this:</p>
  
  <pre><code>                  DD_PRICE  CAPI_PRICE
  DATE                                   
  2013-09-19 20:55:00  3.516  3.516
  2013-09-19 20:55:00  3.516  3.516
  2013-09-19 20:55:00  3.516  3.516
  2013-09-19 20:55:00 -4.476 -4.476
  </code></pre>
  
  <p>How do I get this done? Tried different combos of <code>merge</code> and <code>join</code> parameters but I can't get it to work! </p>