From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.org!not-for-mail From: "Pascal J. Bourguignon" Newsgroups: gmane.emacs.help Subject: Re: random predicate function Date: Mon, 13 Dec 2010 19:38:19 +0100 Organization: Informatimago Message-ID: <87y67tplgk.fsf@kuiper.lan.informatimago.com> References: <87mxo9r8xg.fsf@kuiper.lan.informatimago.com> NNTP-Posting-Host: lo.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-Trace: dough.gmane.org 1292265795 26619 80.91.229.12 (13 Dec 2010 18:43:15 GMT) X-Complaints-To: usenet@dough.gmane.org NNTP-Posting-Date: Mon, 13 Dec 2010 18:43:15 +0000 (UTC) To: help-gnu-emacs@gnu.org Original-X-From: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane.org@gnu.org Mon Dec 13 19:43:11 2010 Return-path: Envelope-to: geh-help-gnu-emacs@m.gmane.org Original-Received: from lists.gnu.org ([199.232.76.165]) by lo.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1PSDMc-0001H6-Ro for geh-help-gnu-emacs@m.gmane.org; Mon, 13 Dec 2010 19:43:11 +0100 Original-Received: from localhost ([127.0.0.1]:39162 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1PSDMc-0002rH-CX for geh-help-gnu-emacs@m.gmane.org; Mon, 13 Dec 2010 13:43:10 -0500 Original-Path: usenet.stanford.edu!fu-berlin.de!uni-berlin.de!individual.net!not-for-mail Original-Newsgroups: gnu.emacs.help Original-Lines: 28 Original-X-Trace: individual.net 9KmF+UZwXf9605N+J86K6wmczcaDTgEyy28yjUP15xrDEz0TGl Cancel-Lock: sha1:N2YxMTExZDJmOTY1YzE3MTkzMjhlNWI0YzRiYzExMWFiYTZmZjRlNA== sha1:K0qpXRNCXd8kKkYKEkum0jsC3x4= Face: iVBORw0KGgoAAAANSUhEUgAAADAAAAAwAQMAAABtzGvEAAAABlBMVEUAAAD///+l2Z/dAAAA oElEQVR4nK3OsRHCMAwF0O8YQufUNIQRGIAja9CxSA55AxZgFO4coMgYrEDDQZWPIlNAjwq9 033pbOBPtbXuB6PKNBn5gZkhGa86Z4x2wE67O+06WxGD/HCOGR0deY3f9Ijwwt7rNGNf6Oac l/GuZTF1wFGKiYYHKSFAkjIo1b6sCYS1sVmFhhhahKQssRjRT90ITWUk6vvK3RsPGs+M1RuR mV+hO/VvFAAAAABJRU5ErkJggg== X-Accept-Language: fr, es, en X-Disabled: X-No-Archive: no User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/23.2 (gnu/linux) Original-Xref: usenet.stanford.edu gnu.emacs.help:183220 X-BeenThere: help-gnu-emacs@gnu.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Users list for the GNU Emacs text editor List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Original-Sender: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane.org@gnu.org Errors-To: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane.org@gnu.org Xref: news.gmane.org gmane.emacs.help:77462 Archived-At: Tyler Smith writes: > "Pascal J. Bourguignon" writes: > >> >> You shoud not use sort to randomize, because it's suboptimal >> [ O(n*log(n)) at best instead of O(n) ]. >> >> And foremost, you should not use a predicate that is not a total order >> because this usually gives invalid results. > > I don't know what a 'total order' means. Is the result of the predicate > invalid or the actual sorting? http://en.wikipedia.org/wiki/Total_order Actually, it should even be a strict total order, that is, it must be a < operator, not a <= operator. If you have cycles such as: a < b < a then some sort algorithms may not terminate. When sorting lists, some algorithms could truncate the result. -- __Pascal Bourguignon__ http://www.informatimago.com/ A bad day in () is better than a good day in {}.