title: Find all duplicate rows in a pandas dataframe
body: <p>I would like to be able to get the indices of all the instances of a duplicated row in a dataset without knowing the name and number of columns beforehand. So assume I have this: </p>
  
  <pre><code>     col
  1  |  1
  2  |  2
  3  |  1
  4  |  1
  5  |  2
  </code></pre>
  
  <p>I'd like to be able to get <code>[1, 3, 4]</code> and <code>[2, 5]</code>. Is there any way to achieve this? It sounds really simple, but since I don't know the columns beforehand I can't do something like <code>df[col == x...]</code>.</p>