参考
http://blog.anekipedia.com/cus/%E8%A8%98%E4%BA%8B%E4%B8%80%E8%A6%A7%E3%82%92%E3%82%BD%E3%83%BC%E3%83%88%EF%BC%88%E4%B8%A6%E3%81%B3%E6%9B%BF%E3%81%88%EF%BC%89%E3%81%99%E3%82%8B.html
http://ateitexe.com/wordpress-archive-sort-popular/
http://takahashifumiki.com/web/programing/1829/