title: Split a list every nth element
body: <p>I would like to split a list regularly every n elements. For example:</p>
  
  <pre><code>a &lt;- 1:9
  </code></pre>
  
  <p>Then split the list every 3 elements.</p>
  
  <p>Result:</p>
  
  <pre><code>[[1]]
  [1] 1 2 3
  
  [[2]]
  [1] 4 5 6
  
  [[3]]
  [1] 7 8 9
  </code></pre>