title: Repeating elements in a dataframe
body: <p>Hi all I have the following dataframe:</p>
  
  <pre><code>A | B | C
  1   2   3 
  2   3   4 
  3   4   5
  4   5   6
  </code></pre>
  
  <p>And I am trying to only repeat the last two rows of the data so that it looks like this:</p>
  
  <pre><code>A | B | C
  1   2   3 
  2   3   4 
  3   4   5
  3   4   5
  4   5   6
  4   5   6
  </code></pre>
  
  <p>I have tried using append, concat and repeat to no avail.</p>
  
  <pre><code>repeated = lambda x:x.repeat(2)
  df.append(df[-2:].apply(repeated),ignore_index=True)
  </code></pre>
  
  <p>This returns the following dataframe, which is incorrect:</p>
  
  <pre><code>A | B | C
  1   2   3 
  2   3   4 
  3   4   5
  4   5   6
  3   4   5
  3   4   5
  4   5   6
  4   5   6
  </code></pre>