Anchor in URL when using Symfony's redirect function
$this->redirect($this->generateUrl('route', array('id' => $id)) . '#anchor7');
UPDATE:
In Symfony 3.2 you can do this:
// generating a URL with a fragment (/settings#password)$this->redirectToRoute('user_settings', ['_fragment' => 'password']);
See https://symfony.com/blog/new-in-symfony-3-2-routing-improvements
Using router :
$router->generateUrl('awesome_route') . '#comment-2';
This method is used by Fabien Potencier : https://github.com/symfony/symfony/issues/3910#issuecomment-5110238