title: Identifying duplicate pairs in python pandas
body: <p>The function <code>pd.duplicated()</code> gives you a boolean series indicating which rows in a dataframe are duplicated like below:</p>
  
  <pre><code>0     False
  1     False
  2     False
  3     False
  4      True
  5     False
  6      True
  7      True
  8      True
  9      True
  10     True
  dtype: bool
  </code></pre>
  
  <p>It however does not tell you which row the duplicates are duplicates of. 
  Index 4 for example could be a duplicate of 0,1,2,3 or 5. </p>
  
  <p>Is there a clever way of identifying which rows are duplicated and what these rows are duplicates of?</p>