public function get_samples($sampleids) {
        global $DB;

        list($sql, $params) = $DB->get_in_or_equal($sampleids, SQL_PARAMS_NAMED);
        $users = $DB->get_records_select('user', "id $sql", $params);

        $userids = array_keys($users);
        $sampleids = array_combine($userids, $userids);

        $users = array_map(function($user) {
            return ['user' => $user, 'context' => \context_user::instance($user->id)];
        }, $users);

        // No related data attached.
        return [$sampleids, $users];
    }