wordpress tag archive, sort order with custom post type

Question

I added this code added to funtions.php

function tc_tag_for_cpt($query) {
  if(is_tag() && empty( $query->query_vars['suppress_filters'] ) && !is_admin()) {
    $post_type = get_query_var('post_type');
    $post_type = ($post_type) ?  $post_type : array('resources','post','page');     //,'nav_menu_item'
    $query->set('post_type',$post_type);
    return $query;
  }
}
add_filter( 'posts_orderby', 'sort_query_by_post_type', 10, 2 );
function sort_query_by_post_type( $sortby, $thequery ) {
    if(is_tag() && empty( $query->query_vars['suppress_filters'] ) && !is_admin()) {
        $thequery->set('orderby','post_type');
        if ( !empty($thequery->query_vars['post_type']) && isset($thequery->query_vars['orderby']) && $thequery->query_vars['orderby'] == 'post_type' )
            $sortby = "find_in_set(post_type, '" . implode( ',', $thequery->query_vars['post_type'] ) . "')";
    }
    return $sortby;
}

which is supposed to display results on the tag archive sorted by post type (resources is a custom post type). It does this but an error message appears on the top of the screen:

"Warning: implode() [function.implode]: Invalid arguments passed in /home/csleh3/public_html/sandbox/wp-content/themes/aodmarketing/functions.php on line 279"

which is the "implode" line.

My goal is to have the results on the tag archive sort the list by post type, not date or title.

Answer 1

$thequery->query_vars['post_type'] will return the specific post_type as a string like post . You can't implode that.

You should just be able to remove the part about trying to implode it:

$sortby = "find_in_set(post_type, '" . $thequery->query_vars['post_type'] . "')";