title: array_map and append string to elements of an array
body: <p>I have an array like this:</p>
  
  <pre><code>$a = array('aa', 'bb', 'cc', 'dd');
  </code></pre>
  
  <p>I want to add the 'rq' string at the beginning of all the elements of the array. Is it possible to do it by calling array_map() on this array?</p>