title: Extract year from date
body: <p>How can I remove the first elements from a variable, especially if this variable has a special characters. For example, I have the following column:</p>
  
  <pre><code>Date
  01/01/2009
  01/01/2010
  01/01/2011
  01/01/2012
  </code></pre>
  
  <p>I need to have a new column like the following:</p>
  
  <pre><code>Date
  2009
  2010
  2011
  2012
  </code></pre>