title: How to increase by 1 all keys in an array?
body: <p>What is the simplest solution to increase by 1 all keys in an array?</p>
  
  <p><strong>BEFORE:</strong></p>
  
  <pre><code>$arr[0] = 'a';
  $arr[1] = 'b';
  $arr[2] = 'c';
  </code></pre>
  
  <p><strong>AFTER:</strong></p>
  
  <pre><code>$arr[1] = 'a';
  $arr[2] = 'b';
  $arr[3] = 'c';
  </code></pre>