title: Get a key from a session array
body: <p>I have an array that is stored in a session like so:</p>
  
  <pre><code>$_SESSION['shortlistArray'][2];
  </code></pre>
  
  <p>Outputs</p>
  
  <pre><code>Peter
  </code></pre>
  
  <p>But how do I do this the other way round and use 'Peter' to get the array key?</p>