I’m trying to add a sortable column to the Users screen for one of my xProfile fields.

I have it working but it’s throwing a notice: Notice: Array to string conversion in /srv/www/server/wp-admin/includes/class-wp-users-list-table.php on line 582

Here is the code I’ve added to a custom plugin:

// Add the custom column

function wpmeo_add_user_columns( $column ) 
{
     $column['Country'] = 'Country';

     return $column;
}
add_filter( 'manage_users_columns', 'wpmeo_add_user_columns' );

// Make the custom column sortable

function wpmeo_sortable_user_columns( $columns )
{
    $columns['Country'] = 'country';

    return $columns;
}
add_filter( 'manage_users_sortable_columns', 'wpmeo_sortable_user_columns', 10, 3 );

// Provide the value of the custom column

function wpmeo_user_columns( $value, $column_name, $id ) 
{
    if( 'Country' == $column_name ) 
    {
        $new_column = xprofile_get_field_data( 'Country', $id );
        return $new_column;
    }
}
add_action( 'manage_users_custom_column', 'wpmeo_user_columns', 10, 3 );

// Sort the custom column asc & desc

function my_wpmeo_pre_user_query($user_search)
{
    global $wpdb, $current_screen;

    // Only filter in the admin
    if ( ! is_admin() )
        return;

    // Only filter on the users screen
    if ( ! ( isset( $current_screen ) && 'users' == $current_screen->id ) )
        return;

    $vars = $user_search->query_vars;

    if('country' == $vars['orderby'])
    {
        $user_search->query_from .= " INNER JOIN {$wpdb->usermeta} m1 ON {$wpdb->users}.ID=m1.user_id AND (m1.meta_key='country')"; 
        $user_search->query_orderby = ' ORDER BY UPPER(m1.meta_value) '. $vars['order'];
    } 
}
add_action('pre_user_query','my_wpmeo_pre_user_query');