From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.org!not-for-mail From: Kevin Rodgers Newsgroups: gmane.emacs.help Subject: Re: Incredible shrinking list.... Date: Fri, 17 Oct 2008 22:15:56 -0600 Message-ID: References: <20081017204742.GB1614@drmemory.local> NNTP-Posting-Host: lo.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-Trace: ger.gmane.org 1224303386 14780 80.91.229.12 (18 Oct 2008 04:16:26 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Sat, 18 Oct 2008 04:16:26 +0000 (UTC) To: help-gnu-emacs@gnu.org Original-X-From: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane.org@gnu.org Sat Oct 18 06:17:26 2008 connect(): Connection refused 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 4.50) id 1Kr3Fl-0005NM-84 for geh-help-gnu-emacs@m.gmane.org; Sat, 18 Oct 2008 06:17:25 +0200 Original-Received: from localhost ([127.0.0.1]:37837 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1Kr3Ef-0001Wt-PP for geh-help-gnu-emacs@m.gmane.org; Sat, 18 Oct 2008 00:16:17 -0400 Original-Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1Kr3EO-0001Vi-VQ for help-gnu-emacs@gnu.org; Sat, 18 Oct 2008 00:16:00 -0400 Original-Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43) id 1Kr3EN-0001U1-7A for help-gnu-emacs@gnu.org; Sat, 18 Oct 2008 00:16:00 -0400 Original-Received: from [199.232.76.173] (port=59574 helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1Kr3EN-0001Tx-0c for help-gnu-emacs@gnu.org; Sat, 18 Oct 2008 00:15:59 -0400 Original-Received: from main.gmane.org ([80.91.229.2]:53742 helo=ciao.gmane.org) by monty-python.gnu.org with esmtps (TLS-1.0:RSA_AES_256_CBC_SHA1:32) (Exim 4.60) (envelope-from ) id 1Kr3EN-0002HU-3t for help-gnu-emacs@gnu.org; Sat, 18 Oct 2008 00:15:59 -0400 Original-Received: from list by ciao.gmane.org with local (Exim 4.43) id 1Kr3EG-000133-3B for help-gnu-emacs@gnu.org; Sat, 18 Oct 2008 04:15:52 +0000 Original-Received: from c-67-161-145-183.hsd1.co.comcast.net ([67.161.145.183]) by main.gmane.org with esmtp (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Sat, 18 Oct 2008 04:15:52 +0000 Original-Received: from kevin.d.rodgers by c-67-161-145-183.hsd1.co.comcast.net with local (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Sat, 18 Oct 2008 04:15:52 +0000 X-Injected-Via-Gmane: http://gmane.org/ Original-Lines: 51 Original-X-Complaints-To: usenet@ger.gmane.org X-Gmane-NNTP-Posting-Host: c-67-161-145-183.hsd1.co.comcast.net User-Agent: Thunderbird 2.0.0.17 (Macintosh/20080914) In-Reply-To: <20081017204742.GB1614@drmemory.local> X-detected-operating-system: by monty-python.gnu.org: GNU/Linux 2.6, seldom 2.4 (older, 4) 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:58897 Archived-At: Scott wrote: > Hi, > > I am very much a newbie, so forgive if this is a stupid question. > > I am trying to write a function which returns a randomized permutation > of a certain number of items. Here is my stab at it, and the problem > which baffles me: > > > (defun pick-ten () > "Pick a series of ten unique random numbers from 0-9. > You should ensure that random is properly 'seeded', as eg: > (random t) > prior to using this function." > (let ((all-ten '(0 1 2 3 4 5 6 7 8 9)) ;initial list > (rnd-list '()) ;return value > (nxt 0)) ;placeholder for current number > (while all-ten ;step through the list > (setq all-ten ;trim by > (delq ;deleting selected number > (setq nxt ;but remember number for later > (car > (nthcdr (mod (random)(length all-ten)) all-ten) > ) > ) all-ten)) > (setq rnd-list (cons nxt rnd-list)) ;and put into the return value > ) > rnd-list ;now return it. > )) > > ;; works fine on the first evaluation, > ;; but the series somehow shrinks with subsequent calls! > ;; what am I doing wrong???! > ;; > (pick-ten)(3 2 9 7 1 6 0 5 8 4) > (pick-ten)(1 0 2 3) > (pick-ten)(0 1) > (pick-ten)(0) Probably destructively modifying a constant -- try this: (let ((all-ten (list 0 1 2 3 4 5 6 7 8 9)) ;initial list or this: (setq all-ten (remq ... all-ten)) -- Kevin Rodgers Denver, Colorado, USA