title: Sorting list of lists by the first element of each sub-list
body: <p>How to sort a list of lists according to the first element of each list?</p>
  
  <p>For example, giving this unsorted list:</p>
  
  <pre><code>[[1,4,7],[3,6,9],[2,59,8]]
  </code></pre>
  
  <p>The sorted result should be:</p>
  
  <pre><code>[[1,4,7],[2,59,8],[3,6,9]]
  </code></pre>