Remove aside posts from menu

Hi,

I have successfully stopped ‘aside’ posts being shown in my blogs menu (using default left side-bar setup) by adding a small piece of code in wp-includes/default-widgets.php.

However, this means altering a core script so I am wondering if anyone can tell me how to achieve this by using a filter?

I am using the twentyfourteen theme and have a child theme setup.

The code I have altered is in ‘class WP_Widget_Recent_Posts extends WP_Widget’ in ‘public function __construct()’

while ( $r->have_posts() ) : $r->the_post(); 

    if(get_post_format( $r->ID ) == 'aside'){
        continue;
    }

    // build menu items

   // other WordPress code

}  // End while loop

Thanks for your help.

My blog is at yew2.com/wordpress. It is not yet live.