CAllUser::GetUserGroup

static function GetUserGroup($ID)
{
	$ID = (int)$ID;
	if (!isset(self::$userGroupCache[$ID]))
	{
		$arr = [];
		$res = static::GetUserGroupEx($ID);
		while ($r = $res->Fetch())
		{
			$arr[] = $r["GROUP_ID"];
		}

		self::$userGroupCache[$ID] = $arr;
	}

	return self::$userGroupCache[$ID];
}