title: PHP - Sort array with mixed types
body: <p>I have a php array with mixed types like this :</p>
  
  <pre><code>  $length = array (15, 3, 5, '-');
  </code></pre>
  
  <p>and I want to sort it to obtain a list of values sorted like this : '-', 3, 5, 15</p>
  
  <p>How can I do that ?</p>
  
  <p>Thanks a lot.</p>