Attendees list filter

function get_filtered_riderslist( $rider_category = false ) {

    if ( false != $rider_category ) {
        global $EM_Event;
        $all_bookings = $EM_Event->get_bookings();
        if ( $all_bookings ) {
            $counter        = 0;
            $attendees_list = '';

            foreach ( $all_bookings as $EM_Booking ) {
                $attendee_info = $EM_Booking->booking_meta[ 'attendees' ];
                $member        = $EM_Booking->get_person()->ID;
                $member_data   = get_userdata( $member );
                $rider_name    = $EM_Booking->get_person()->get_name();
                $nationality   = get_user_field( 'nationality', $member );

                foreach ( $attendee_info as $attendees ) {
                    foreach ( $attendees as $attendee ) {
                        foreach ( $attendee as $categories ) {
                            foreach ( $categories as $category ) {
                                // outputs category name
                                if ( strpos( $category, $rider_category ) !== false ) {
                                    $counter++;
                                    // add booking to var
                                    $attendees_list        .= '<tr>';
                                    $attendees_list        .= '<td>' . $counter . '.</td>';
                                    $attendees_list        .= '<td><a href="' . home_url() . '/member/' . $member_data->user_nicename . '/">' . $rider_name . '</a> (' . $nationality . ')</td>';
                                    $attendees_list        .= '</tr>';
                                }
                            }
                        }
                    }
                }
            }
        }
    }

    return $attendees_list;
}