title: Append observation at end of row from another column in R
body: <p>I have data with 900 rows and 400 columns. Each two column carry particular information. Let me say, there are A B C D column, I will like append C and C column just end of A and B column. </p>
  
  <p>For example: </p>
  
  <hr>
  
  <pre><code>A   B   C   D   E   F  
  3   4   5   6   7   8
  9   10  11  12  13  14
  </code></pre>
  
  <p>to change to </p>
  
  <pre><code>Column 1   Column 2 
  3            4 
  9            10
  5            6
  11           12
  7            8
  13           14
  </code></pre>