Path: csiph.com!x330-a1.tempe.blueboxinc.net!usenet.pasdenom.info!aioe.org!news-transit.tcx.org.uk!rt.uk.eu.org!newsfeed.xs4all.nl!newsfeed5.news.xs4all.nl!xs4all!post.news.xs4all.nl!not-for-mail Return-Path: X-Original-To: python-list@python.org Delivered-To: python-list@mail.python.org X-Spam-Status: OK 0.031 X-Spam-Evidence: '*H*': 0.94; '*S*': 0.00; 'python,': 0.01; 'behave': 0.07; 'python': 0.08; 'url:pypi': 0.08; 'to:addr:comp.lang.python': 0.09; 'accesses': 0.16; 'computation': 0.16; 'integers.': 0.16; 'subject:independent': 0.16; 'cc:addr :python-list': 0.16; 'wrote:': 0.18; 'computing': 0.18; 'yet.': 0.18; 'cc:no real name:2**0': 0.20; "doesn't": 0.22; 'header:In- Reply-To:1': 0.22; 'table.': 0.23; 'tree': 0.25; 'cc:addr:gmail.com': 0.28; 'needed,': 0.28; 'sound': 0.28; 'message-id:@mail.gmail.com': 0.28; 'elements': 0.29; 'mapping': 0.29; 'cc:addr:python.org': 0.29; 'hash': 0.30; 'received:mail- bw0-f46.google.com': 0.30; 'least': 0.30; 'subject:?': 0.31; "i'll": 0.31; 'go.': 0.32; 'pure': 0.32; 'list': 0.32; 'received:209.85.214': 0.32; "isn't": 0.33; 'sort': 0.33; "won't": 0.33; 'agree': 0.33; 'too': 0.34; 'things': 0.34; 'operations': 0.35; 'url:python': 0.36; 'cc:2**1': 0.36; 'members': 0.37; 'two': 0.37; 'but': 0.37; 'list,': 0.37; 'received:google.com': 0.37; "there's": 0.37; 'could': 0.37; 'doing': 0.38; 'bunch': 0.38; 'monday,': 0.38; 'some': 0.38; 'received:209.85': 0.38; 'url:org': 0.39; 'should': 0.39; "it's": 0.40; 'received:209': 0.40; 'might': 0.40; 'once': 0.60; 'range': 0.61; 'more': 0.61; '2011': 0.61; 'your': 0.61; 'life': 0.64; 'url:0': 0.67; 'methods:': 0.67; 'often,': 0.84; 'ordered.': 0.84; 'scatter': 0.84; 'fast,': 0.91; 'sum.': 0.91 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type; bh=7zMAm+ikL0Ndd7zziZ61wYBlfiyjVBZPJEEYegnyqTI=; b=Ad6hxyXoc7NTAHii4mxzp7C5T0Aui6dTD84ArB6i3EJ03wQUg7vuPr62Sron1kd1F5 3NpK0nF10Ss7YkMNGdJgbJuIGZqP3CecqV+uOmFQsTJxdXI5SNqLDngVkT7xYtHxqbly KlJi1MgahcWM1MoqHtVB8BGXRbu2zovk87yP0= MIME-Version: 1.0 In-Reply-To: <952995.674.1323086974877.JavaMail.geo-discussion-forums@preu18> References: <952995.674.1323086974877.JavaMail.geo-discussion-forums@preu18> Date: Mon, 5 Dec 2011 15:05:26 -0800 Subject: Re: order independent hash? From: Dan Stromberg To: comp.lang.python@googlegroups.com Content-Type: text/plain; charset=ISO-8859-1 Cc: Neal Becker , python-list@python.org X-BeenThere: python-list@python.org X-Mailman-Version: 2.1.12 Precedence: list List-Id: General discussion list for the Python programming language List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Newsgroups: comp.lang.python Message-ID: Lines: 42 NNTP-Posting-Host: 2001:888:2000:d::a6 X-Trace: 1323126329 news.xs4all.nl 6871 [2001:888:2000:d::a6]:47556 X-Complaints-To: abuse@xs4all.nl Xref: x330-a1.tempe.blueboxinc.net comp.lang.python:16695 On 12/5/11, 88888 Dihedral wrote: > On Monday, December 5, 2011 1:50:08 PM UTC+8, Dan Stromberg wrote: >> Two methods: >> 1) If you need your hash only once in an infrequent while, then save >> the elements in a list, appending as needed, and sort prior to >> hashing, as needed >> >> 2) If you need your hash more often, you could keep your elements in a >> treap or red-black tree; these will maintain sortedness throughout the >> life of the datastructure. >> >> 3) If A bunch of log(n) or n or nlog(n) operations doesn't sound >> appealing, then you might try this one: Create some sort of mapping >> from your elements to the integers. Then just use a sum. This won't >> scatter things nearly as well as a cryptographic hash, but it's very >> fast, because you don't need to reevaluate some of your members as you >> go. >> >> HTH >> > A sorted list can behave like a hash table. This is of O(log(n)) in > accesses > of n items in theory. > > I agree with you a hash key computation method too slow than a list of n > items in accesses for a range of n items should be reloadable. > > But this is not supported in Python yet. > > For tedious trivial jobs of non-heavy computing , I'll opt for easy use. A sorted list is O(log(n)) for lookups, but O(n) for insertions. If you have a process doing both, the table operations are O(n). A hash table that isn't overfilled is O(1) for lookups, O(1) for insertions. But this is not ordered. Here's a straightforward treap implementation for python, with pure python and cython versions: http://pypi.python.org/pypi/treap/0.995 There's also at least one red-black tree implementation available.