public static function make_topic_map($pids)
{
$result = Dbl::qe("select paperId, group_concat(topicId) as topicIds from PaperTopic where paperId ?a group by paperId", $pids);
$topic_map = Dbl::fetch_map($result);
foreach ($topic_map as $pid => &$t) {
$t = explode(",", $t);
foreach ($t as &$x) {
$x = (int) $x;
}
}
return $topic_map;
}
