From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.org!not-for-mail From: =?UTF-8?B?QW5kcmVhcyBSw7ZobGVy?= Newsgroups: gmane.emacs.help Subject: Re: how to access a large datastructure efficiently? Date: Thu, 04 Mar 2010 16:49:23 +0100 Message-ID: <4B8FD683.6050308@easy-emacs.de> References: <873a0gshb6.fsf@tux.homenetwork> <87y6i8r1j3.fsf@tux.homenetwork> <4B8F6BBC.2000607@easy-emacs.de> <87lje8z70e.fsf@tux.homenetwork> 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 1267717662 16385 80.91.229.12 (4 Mar 2010 15:47:42 GMT) X-Complaints-To: usenet@dough.gmane.org NNTP-Posting-Date: Thu, 4 Mar 2010 15:47:42 +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 16:47:37 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 1NnDGy-0001Eg-Gi for geh-help-gnu-emacs@m.gmane.org; Thu, 04 Mar 2010 16:47:36 +0100 Original-Received: from localhost ([127.0.0.1]:41231 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1NnDGx-00072t-VK for geh-help-gnu-emacs@m.gmane.org; Thu, 04 Mar 2010 10:47:35 -0500 Original-Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1NnDGV-00070V-2f for help-gnu-emacs@gnu.org; Thu, 04 Mar 2010 10:47:07 -0500 Original-Received: from [140.186.70.92] (port=51388 helo=eggs.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1NnDGT-0006yn-Sc for help-gnu-emacs@gnu.org; Thu, 04 Mar 2010 10:47:06 -0500 Original-Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.69) (envelope-from ) id 1NnDGS-0004OW-O2 for help-gnu-emacs@gnu.org; Thu, 04 Mar 2010 10:47:05 -0500 Original-Received: from moutng.kundenserver.de ([212.227.126.187]:64380) by eggs.gnu.org with esmtp (Exim 4.69) (envelope-from ) id 1NnDGS-0004Nl-Dn for help-gnu-emacs@gnu.org; Thu, 04 Mar 2010 10:47:04 -0500 Original-Received: from [192.168.178.27] (p54BEBACF.dip0.t-ipconnect.de [84.190.186.207]) by mrelayeu.kundenserver.de (node=mreu1) with ESMTP (Nemesis) id 0MAihL-1Nt2101c6d-00C1yy; Thu, 04 Mar 2010 16:47:01 +0100 User-Agent: Thunderbird 2.0.0.19 (X11/20081227) In-Reply-To: <87lje8z70e.fsf@tux.homenetwork> X-Provags-ID: V01U2FsdGVkX18cQzLBn3zgMt0/2GjKiqUP7X/dkSNxeNawfxd RVx9W1Nr86CeLyIw2F/nlUwoHsoam8aQBf3FT1L3xzNXofZp/g 1ICD6Bi1n+5urVwVdoZgu/ZA3/eTcZMW8QWE2AMg8I= X-detected-operating-system: by eggs.gnu.org: Genre and OS details not recognized. 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:72364 Archived-At: 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 "=" Andreas >> Thanks BTW, very interesting >> >> Andreas >> >> >> >