Listing posts in groups

On my archive pages I need to list the content in category groups. In order to do that I use “rewind_posts();” and run multiple loops like the one below.


while (have_posts()) : the_post();
if (in_category('8')) {
include "includes/post.php";
}
endwhile;


Now, when there is no content in that category it is an empty space. And if I do an else statement in my if(in_category(‘8’)) conditional I get as many lines as there are total posts.

Is there a way for me to say, if there are no posts in a category, to display a message?

Example