title: Python list manipulation
body: <p>I've got a python list</p>
  
  <pre><code>alist = [ [0, 4, 5, 5], [2, 2, 4, 5], [6, 7, 8,13]], [ [3, 4, 5, 5], [2, 2, 4, 5], [6, 7, 8,999] ]
  </code></pre>
  
  <p>I need the result is</p>
  
  <pre><code>alist = [[0,4,8,13], [3, 4, 8, 999]]
  </code></pre>
  
  <p>It means first two and last two numbers in each alist element.</p>
  
  <p>I need a fast way to do this as the list could be huge.</p>