title: Can Twig count the array lenght with a filter parameter
body: <p>I have an Account object that contains an one-to-many relation with the newsbrief members. In Twig a want to show the quantity of members. I know that I can show the quantity with the following code:</p>
  
  <pre><code>{{ account.mailList|length }}
  </code></pre>
  
  <p>Only the mailList contains also inactive members. With these members their field active is false. Is there a way to filter them out? Is this way of working slowing down the application?</p>