title: What is a general way to break up a vector into a list
body: <p>Suppose we have a vector:</p>
  
  <pre><code>x &lt;- c(1,1,1,2,2,2,2,2,4,4,2,2,2,2)
  </code></pre>
  
  <p>What is a function that can take <code>x</code> and return <code>l</code>, where <code>l</code> is equal to</p>
  
  <pre><code>[[1]]
  [1] 1 1 1
  [[2]]
  [1] 2 2 2 2 2
  [[3]]
  [1] 4 4
  [[4]]
  [1] 2 2 2 2
  </code></pre>