BuddyPress.org

In other words, looking to the database, I basically need to add a “sort by” function that sorts users by The avg of a field of the avtivity table. That is, I don’t sort by a x profile field but by the avg of a value of The activity table of my DB. Any idea on how Can i do that, or any piece of code from which i can start to fine The soluto?
Thanks!!

I tryed to work also with this solution (provided by @shanebp too):
https://buddypress.org/support/topic/creating-a-new-order-by-filter-in-groups-loop-with-custom-sql/
but I do not obtain to order members by rating.. is this the right approach??

function antares_members_filter_options() {
    echo '<option value="rating">rating</option>';
}
add_action( 'bp_members_directory_order_options', 'antares_members_filter_options' );

function antares_ajax_querystring( $query_string, $object ) {

	if ( 'members' != $object ) 
		return $query_string;

	if ( ! bp_is_members_directory() ) 
		return $query_string;
	
	$query_args = wp_parse_args( $query_string, array() );

        $page = $query_args['page'];

	if( isset( $query_args['action'] ) && $query_args['action'] == 'rating' ) {
	
		$query_args = array();
		$query_args['page'] = $page;
		$query_args['orderby'] = 'rating';		
		$query_args['order'] = 'ASC';			
		$query_args['include'] = antares_get_members(); 
		$query_string = http_build_query( $query_args );

	}

	return $query_string;

}
add_filter( 'bp_ajax_querystring', 'antares_ajax_querystring', 32, 2 );

function antares_get_members() {
    global $wpdb;

        $sql = "SELECT 
					a.ID as id, a.user_login AS name, a.display_name AS displayname, AVG(star) AS rating, COUNT(star) AS reviews
				FROM 
					{$wpdb->prefix}users AS a
				LEFT JOIN 
					{$wpdb->prefix}bp_activity AS b ON a.ID = b.usercheck
				WHERE 
					(b.is_activated is null or b.is_activated=1)
				GROUP BY 
					id
				ORDER BY 
					rating DESC";
    
$buff = array();

$result = $wpdb->get_results( $sql , OBJECT );

		foreach ($result as $row) {
			$buff[]= $row->id ;
		}
		
$query_str= implode (',', $buff);
return $query_str;
}

Thank you Shanebp
I tried the following steps (below is the final code):
-I started from the basic random code
-I introduced the function to create and pass #sql (like Ninja Warrior trick code)
but it seems not working.. Can you help me please (I’m really trying everithing..)?
Thanks

<?php
 
// Exit if accessed directly
if ( !defined( 'ABSPATH' ) ) exit;
 
class BP_Loop_Filters {
 
    
    public function __construct() {
        $this->setup_actions();
    }
 
    private function setup_actions() {
        /**
         * Adds the Rating order to the select boxes of the Members directory pages
         */
        // Members component is core, so it will be available
        add_action( 'bp_members_directory_order_options', array( $this, 'rating_order' ) );
 
    }
 
    public function rating_order() {
       
	global $wpdb;

	$sql = "SELECT
                 a.ID as id, a.user_nicename AS name, a.display_name AS displayname, AVG(star) AS rating, COUNT(star) AS reviews
             FROM {$wpdb->prefix}users AS a
             LEFT JOIN {$wpdb->prefix}bp_activity AS b ON a.ID = b.usercheck
             WHERE (b.is_activated is null or b.is_activated=1)
             GROUP BY id
             ORDER BY rating DESC";
    var_dump( $sql );

	return $sql;

    }
 
}
 
function bp_loop_filters() {
    return new BP_Loop_Filters();
}
 
add_action( 'bp_include', 'bp_loop_filters' );