title: Move certain data from first column, to the last column on the row above
body: <p>I have a data frame that comes in the following format</p>
  
  <pre><code>   c1  c2  c3
  1   A   1   D
  2   A   2   D
  3   A   3   D
  4   X   4   D
  5   A   5   D
  6   X   6   D
  7   X   7   D
  8   A   8   D
  </code></pre>
  
  <p>I need to make it so that any rows with "X" in <code>c1</code> are merged into <code>c3</code> of the row above, like below</p>
  
  <pre><code>   c1  c2        c3
  1   A   1         D
  2   A   2         D
  3   A   3      DX4D
  4   A   5   DX6DX7D
  5   A   8         D
  </code></pre>
  
  <p>Any ideas?</p>