title: Gather groups of columns
body: <p>I have data from an online survey where respondents go through a series of 5 questions.
  The data I am working at looks like this:</p>
  
  <pre><code>    P1 P2 P3 P4 P5  P1 P2 P3 P4 P5  P1 P2 P3 P4 P5
      1  2  3  4  5   1  2  3  4  5   1  2  3  4  5
      6  7  8  9  10  6  7  8  9  10  6  7  8  9  10
  </code></pre>
  
  <p>The desired output is:</p>
  
  <pre><code>     P1 P2 P3 P4 P5  
       1  2  3  4  5
       6  7  8  9  10
       1  2  3  4  5
       6  7  8  9  10
       1  2  3  4  5
       6  7  8  9  10
  </code></pre>
  
  <p>I have been trying to solve this problem with library tidyr, but i can't understand how to apply it.
  Some advise on this will be really helpful.</p>