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 08:25:52 +0100 Organization: ThierryVolpiatto Message-ID: <87y6i8r1j3.fsf@tux.homenetwork> References: <873a0gshb6.fsf@tux.homenetwork> NNTP-Posting-Host: lo.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-Trace: dough.gmane.org 1267687855 3632 80.91.229.12 (4 Mar 2010 07:30:55 GMT) X-Complaints-To: usenet@dough.gmane.org NNTP-Posting-Date: Thu, 4 Mar 2010 07:30:55 +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 08:30:51 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 1Nn5WE-00046p-Rl for geh-help-gnu-emacs@m.gmane.org; Thu, 04 Mar 2010 08:30:51 +0100 Original-Received: from localhost ([127.0.0.1]:50236 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1Nn5WE-0000PM-8x for geh-help-gnu-emacs@m.gmane.org; Thu, 04 Mar 2010 02:30:50 -0500 Original-Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1Nn5Vm-0000PH-8s for help-gnu-emacs@gnu.org; Thu, 04 Mar 2010 02:30:22 -0500 Original-Received: from [140.186.70.92] (port=46874 helo=eggs.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1Nn5Vl-0000P9-Am for help-gnu-emacs@gnu.org; Thu, 04 Mar 2010 02:30:21 -0500 Original-Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.69) (envelope-from ) id 1Nn5Vk-0002GY-G2 for help-gnu-emacs@gnu.org; Thu, 04 Mar 2010 02:30:21 -0500 Original-Received: from lo.gmane.org ([80.91.229.12]:60359) by eggs.gnu.org with esmtp (Exim 4.69) (envelope-from ) id 1Nn5Vk-0002GR-3V for help-gnu-emacs@gnu.org; Thu, 04 Mar 2010 02:30:20 -0500 Original-Received: from list by lo.gmane.org with local (Exim 4.69) (envelope-from ) id 1Nn5Vj-0003ro-Br for help-gnu-emacs@gnu.org; Thu, 04 Mar 2010 08:30:19 +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 08:30:19 +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 08:30:19 +0100 X-Injected-Via-Gmane: http://gmane.org/ Original-Lines: 56 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: sha1:5UMnF9UOHDt4CrLkaahnTZqWKFA= 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:72353 Archived-At: 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... -- Thierry Volpiatto Gpg key: http://pgp.mit.edu/