title: How to change orders of array?
body: <pre><code>$a = array(0=&gt;'a',1=&gt;'b',2=&gt;'c', 3=&gt;'d');
  </code></pre>
  
  <p>I want to change the order to be <code>3,2,0,1</code>：</p>
  
  <pre><code>$a = array(3=&gt;'d',2=&gt;'c',0=&gt;'a', 1=&gt;'b');
  </code></pre>