function hide_admin_bar_from_front_end(){
if (is_blog_admin()) {
return true;
}
return false;
}
add_filter( 'show_admin_bar', 'hide_admin_bar_from_front_end' );
Edit:
As @Walf suggested in the comments, this could be writen as:
add_filter('show_admin_bar', 'is_blog_admin');