Is there a way to define the $post var outside the loop?

Question

I am trying to speed up a wordpress site by condensing three wp_queries into one. I have a need to seperate categories, so I am making the call and defining 3 arrays to hold the post using a switch, like so:

 $new_query = new WP_Query();
                $new_query->query('post_type=post&paged='.$paged);
                if ( $new_query->have_posts() ) : while ( $new_query->have_posts() ) : $new_query->the_post();              
                $category = choose_one_category(get_the_category());

                switch ($category){
                    case "Category 1":
                        $cat1[] = $post;
                        break;
                    case "Category 2":
                        $cat2[] = $post;
                        break;
                    case "Category 3":
                        $cat3[] = $post;
                        break;
                }


                endwhile; endif;

which leaves me with 3 arrays which with the posts nicely sorted. Now I wish to define the variable $post OUTSIDE the loop so that I can use methods like the_date() & comments_number() without having to rewrite those functions, can anyone help?

I have tried:

                    foreach ($centre as $new_post){
                        $post = $new_post;

                                             include('front_page_loop.php');
                    } 

Where front_page_loop.php is my loop code, but I just get the same post, albeit with different dates

Answer 1

I think setup_postdata($post) (internal) function does that. I failed to find proper documentation for it in Codex (typical), but there are examples with it here and there like in Displaying Posts Using a Custom Select Query.

This test snippet seems to work fine for example code you have in question:

foreach ( $cat1 as $post ) {

    setup_postdata($post);
    printf( 'Post "%s" was posted %s ago<br />',
        get_the_title(),
        human_time_diff( strtotime( get_the_date() ) )
        );
}