From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.org!not-for-mail From: Thierry Volpiatto Newsgroups: gmane.emacs.help Subject: Re: how to access a large datastructure efficiently? Date: Thu, 04 Mar 2010 17:09:35 +0100 Organization: ThierryVolpiatto Message-ID: <87hbowysow.fsf@tux.homenetwork> References: <873a0gshb6.fsf@tux.homenetwork> <87y6i8r1j3.fsf@tux.homenetwork> <4B8F6BBC.2000607@easy-emacs.de> <87lje8z70e.fsf@tux.homenetwork> <4B8FD683.6050308@easy-emacs.de> NNTP-Posting-Host: lo.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit X-Trace: dough.gmane.org 1267725218 16517 80.91.229.12 (4 Mar 2010 17:53:38 GMT) X-Complaints-To: usenet@dough.gmane.org NNTP-Posting-Date: Thu, 4 Mar 2010 17:53:38 +0000 (UTC) To: help-gnu-emacs@gnu.org Original-X-From: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane.org@gnu.org Thu Mar 04 18:53:26 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 1NnFEg-0006pK-8I for geh-help-gnu-emacs@m.gmane.org; Thu, 04 Mar 2010 18:53:22 +0100 Original-Received: from localhost ([127.0.0.1]:54566 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1NnFEf-0006pO-P3 for geh-help-gnu-emacs@m.gmane.org; Thu, 04 Mar 2010 12:53:21 -0500 Original-Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1NnDgm-0002Cd-A7 for help-gnu-emacs@gnu.org; Thu, 04 Mar 2010 11:14:16 -0500 Original-Received: from [140.186.70.92] (port=41074 helo=eggs.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1NnDgk-0002BD-Rb for help-gnu-emacs@gnu.org; Thu, 04 Mar 2010 11:14:15 -0500 Original-Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.69) (envelope-from ) id 1NnDgj-0001Mc-QI for help-gnu-emacs@gnu.org; Thu, 04 Mar 2010 11:14:14 -0500 Original-Received: from lo.gmane.org ([80.91.229.12]:45428) by eggs.gnu.org with esmtp (Exim 4.69) (envelope-from ) id 1NnDgj-0001MD-FN for help-gnu-emacs@gnu.org; Thu, 04 Mar 2010 11:14:13 -0500 Original-Received: from list by lo.gmane.org with local (Exim 4.69) (envelope-from ) id 1NnDgi-0001FB-Bx for help-gnu-emacs@gnu.org; Thu, 04 Mar 2010 17:14:12 +0100 Original-Received: from 43.211.85-79.rev.gaoland.net ([79.85.211.43]) by main.gmane.org with esmtp (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Thu, 04 Mar 2010 17:14:12 +0100 Original-Received: from thierry.volpiatto by 43.211.85-79.rev.gaoland.net with local (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Thu, 04 Mar 2010 17:14:12 +0100 X-Injected-Via-Gmane: http://gmane.org/ Original-Lines: 108 Original-X-Complaints-To: usenet@dough.gmane.org X-Gmane-NNTP-Posting-Host: 43.211.85-79.rev.gaoland.net Face: iVBORw0KGgoAAAANSUhEUgAAADAAAAAwBAMAAAClLOS0AAAAElBMVEUHBARgJRFPS0WbMBTC TSG/uJs0yyVHAAAACXBIWXMAAAsSAAALEgHS3X78AAAACXZwQWcAAAAwAAAAMADO7oxXAAABpUlE QVQ4y3VTQXKDMAyUnD7AwvQOhtxj5N4LFh9ow/+/UtlpM0BczWSS0Wola7UBeEb3+3kJ/5p9ZLz3 UI0n0J0Y4K/lh1nG24FhlJOR2LdSKtpV5gfi/Zd+NdaJBbB4D5N0JnfUIVp6obZURkJwS2a8b9uX AkgxA5gCEcknAH1s2z0DPooWmjGKcJR+HNZt+9bm0GtGRycRuZGs98Ffr02vABWGopIAhmXmxnQN BwBXZjgFLHRoqbfeYxCLWqsjLyKhbEHW+A5nEs699Q2O80ALrgHTmUTy6P0MnKyKQpKHpoNWokxs F0D5VegvWmEozyE6nuMiS98mWzlUQ9bW8qYfqOaFtzWlYCqGeIs6HEyl08jkrxUG9MF5ipXpOOpd ZMoXPPVSLWJiiwNNB+eRSyxJZmQKcacikgucnCRiHuJOLmyYJRDPwOqAvY4pA+Wy+VS8G26BAsdb Ph2Hw7ORy/H0IOG0TnaM8Cp0XrFYyU0v2z8AqkifPVbLZ0qo/gsRg60C7p+8Ov9jrUIxFde+jnAq X42hyp/c+ZcnVyUYBarrqZt3+R8450png3cWKgAAACV0RVh0ZGF0ZTpjcmVhdGUAMjAwOC0wNS0z MVQyMjoxNDoyMiswMjowMK3VBDcAAAAldEVYdGRhdGU6bW9kaWZ5ADIwMDctMTAtMjhUMTc6MDg6 NDgrMDE6MDDLdIcLAAAAEXRFWHRqcGVnOmNvbG9yc3BhY2UAMix1VZ8AAAAgdEVYdGpwZWc6c2Ft cGxpbmctZmFjdG9yADJ4MiwxeDEsMXgxSfqmtAAAAABJRU5ErkJggg== User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/23.1.93 (gnu/linux) Cancel-Lock: sha1:vKZWSbCMEoK9sCk3q4T5aVOoNz0= X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.6 (newer, 3) 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:72365 Archived-At: Andreas Röhler writes: > Thierry Volpiatto wrote: >> Andreas Röhler writes: >> >>> Thierry Volpiatto wrote: >>>> Thierry Volpiatto writes: >>>> >>>>> Hi, >>>>> >>>>> Christian Wittern writes: >>>>> >>>>>> Hi there, >>>>>> >>>>>> Here is the problem I am trying to solve: >>>>>> >>>>>> I have a large list of items which I want to access. The items are in >>>>>> sequential order, but many are missing in between, like: >>>>>> >>>>>> (1 8 17 23 25 34 45 47 50) [in reality, there is a value associated >>>>>> with this, but I took it out for simplicity] >>>>>> >>>>>> Now when I am trying to access with a key that is not in the list, I >>>>>> want to have the one with the closest smaller key returned, so for 6 >>>>>> and 7 this would be 1, but for 8 and 9 this would be 8. >>>>>> >>>>>> Since the list will have thousands of elements, I do not want to simply >>>>>> loop through it but am looking for better ways to do this in Emacs lisp. >>>>>> Any ideas how to achieve this? >>>>> ,---- >>>>> | (defun closest-elm-in-seq (n seq) >>>>> | (let ((pair (loop with elm = n with last-elm >>>>> | for i in seq >>>>> | if (and last-elm (< last-elm elm) (> i elm)) return (list last-elm i) >>>>> | do (setq last-elm i)))) >>>>> | (if (< (- n (car pair)) (- (cadr pair) n)) >>>>> | (car pair) (cadr pair)))) >>>>> `---- >>>>> >>>>> That return the closest, but not the smaller closest, but it should be >>>>> easy to adapt. >>>> Case where your element is member of list, return it: >>>> >>>> ,---- >>>> | (defun closest-elm-in-seq (n seq) >>>> | (let ((pair (loop with elm = n with last-elm >>>> | for i in seq >>>> | if (eq i elm) return (list i) >>>> | else if (and last-elm (< last-elm elm) (> i elm)) return (list last-elm i) >>>> | do (setq last-elm i)))) >>>> | (if (> (length pair) 1) >>>> | (if (< (- n (car pair)) (- (cadr pair) n)) >>>> | (car pair) (cadr pair)) >>>> | (car pair)))) >>>> `---- >>>> For the smallest just return the car... >>>> >>> if n is member of the seq, maybe equal-operator too >>> >>> (<= last-elm elm) >>> >>> is correct? >> >> No, in this case: >> >> if (eq i elm) return (list i) ==> (i) ; which is n >> >> and finally (car pair) ==> n >> > > Hmm, sorry being the imprecise, > aimed at the first form, whose result equals the the second form once implemented this "=" Ok, i understand, yes, we can do what you say and it's more elegant, i just notice also i forget to remove a unuseful else: ,---- | (defun closest-elm-in-seq (n seq) | (let ((pair (loop with elm = n with last-elm | for i in seq | if (and last-elm (<= last-elm elm) (> i elm)) return (list last-elm i) | do (setq last-elm i)))) | (if (< (- n (car pair)) (- (cadr pair) n)) | (car pair) (cadr pair)))) `---- That should work the same. Thanks. ;-) > Andreas > >>> Thanks BTW, very interesting >>> >>> Andreas >>> >>> >>> >> > > > > -- Thierry Volpiatto Gpg key: http://pgp.mit.edu/