title: How to merge 2 vectors alternating indexes?
body: <p>I would like to merge 2 vectors this way :</p>
  
  <pre><code>a = c(1,2,3)
  b = c(11,12,13)
  merged vector : c(1,11,2,12,3,13)
  </code></pre>
  
  <p>How could I do it ?</p>