Path: csiph.com!usenet.pasdenom.info!weretis.net!feeder1.news.weretis.net!feeder4.news.weretis.net!rt.uk.eu.org!newsfeed.xs4all.nl!newsfeed2.news.xs4all.nl!xs4all!newsgate.cistron.nl!newsgate.news.xs4all.nl!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 0.018 X-Spam-Evidence: '*H*': 0.96; '*S*': 0.00; 'mrab': 0.05; 'cc:addr :python-list': 0.11; "wouldn't": 0.14; '1.5,': 0.16; 'from:addr:rosuav': 0.16; 'from:name:chris angelico': 0.16; 'nan': 0.16; 'nans': 0.16; 'somewhere.': 0.16; 'sorted()': 0.16; 'sorting': 0.16; 'sorting.': 0.16; 'elements': 0.16; 'wrote:': 0.18; 'thu,': 0.19; 'seems': 0.21; '>>>': 0.22; 'rules': 0.22; 'cc:addr:python.org': 0.22; 'comparing': 0.24; 'documented': 0.24; 'skip:l 30': 0.24; 'cc:2**0': 0.24; 'sort': 0.25; 'header:In- Reply-To:1': 0.27; 'message-id:@mail.gmail.com': 0.30; "i'm": 0.30; 'end,': 0.31; 'equality': 0.31; 'tuples': 0.31; 'probably': 0.32; 'supposed': 0.32; 'beginning': 0.33; 'case,': 0.35; 'but': 0.35; 'received:google.com': 0.35; 'being': 0.38; 'pm,': 0.38; 'sure': 0.39; 'simple': 0.61; "you're": 0.61; 'happen': 0.63; 'choose': 0.64; 'default': 0.69; 'jul': 0.74; 'special': 0.74; 'subject:For': 0.78; 'to:none': 0.92; 'reliable,': 0.93 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:in-reply-to:references:date:message-id:subject:from:cc :content-type; bh=vA9idHiR5KDhQYVxkQL2HePYzjZTKJ/5HauKbnUyyfY=; b=L6KPnUC4qsqzCAG7JCfxMkFsTx2s0ColgT5tq7/Oz9I/6p2sW+3MzUPggr9JcEkN4W dBGKhScpFX+ljfrh7h4rh41WvUkOhq+mzHULov39e4fLnIVLObIM3N/LW4tkYsTOT2BF u9CQhN9CwdqtD55Bqcx9UO+Oz+I+1/cVJIzz56gz5YqPn+nSkCobi/9HUtjE1ocav5w0 wTeJK93aQnFH/dM9Utxfji7qyoZZrLOHH9sP0s5NQjnUpGwP4+h8VjOXAmzQITI2+/q3 dDxJZuB2mEzY8y8tFThWA5L3rQFkdTZEpSrOkpNHqfYOAWvj295FPYkIa4/if/21IXd3 RPRQ== MIME-Version: 1.0 X-Received: by 10.52.108.234 with SMTP id hn10mr7698102vdb.4.1404992280246; Thu, 10 Jul 2014 04:38:00 -0700 (PDT) In-Reply-To: <53BE78D0.60802@mrabarnett.plus.com> References: <53BC05FB.4050707@jmunch.dk> <53BD70F4.4000504@stoneleaf.us> <53BDAF90.8010709@jmunch.dk> <53BDCA33.3020100@jmunch.dk> <85oawyt4ho.fsf@benfinney.id.au> <53BE78D0.60802@mrabarnett.plus.com> Date: Thu, 10 Jul 2014 21:38:00 +1000 Subject: Re: NaN comparisons - Call For Anecdotes From: Chris Angelico Cc: "python-list@python.org" Content-Type: text/plain; charset=UTF-8 X-BeenThere: python-list@python.org X-Mailman-Version: 2.1.15 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: 27 NNTP-Posting-Host: 2001:888:2000:d::a6 X-Trace: 1404992282 news.xs4all.nl 2941 [2001:888:2000:d::a6]:44026 X-Complaints-To: abuse@xs4all.nl Xref: csiph.com comp.lang.python:74299 On Thu, Jul 10, 2014 at 9:28 PM, MRAB wrote: > I can think of one place where equality of NaNs would be useful: > sorting. > > However, in that use-case, you would also want it to be orderable, > perhaps greater than any other non-NaN float. In that case, you're setting special rules, so you probably want a key-based sort. Since the sorting of tuples works by comparing elements sequentially, it's simple enough: >>> l=[1.0,2.0,1.5,float("nan"),1.7] >>> sorted(l,key=lambda n: (n!=n, n)) [1.0, 1.5, 1.7, 2.0, nan] I'm not sure what's supposed to happen if you just let sorted() go with its default comparisons. It seems to put the nan at the end, but I wouldn't bet on that being reliable, unless it's documented somewhere. Of course, with a key sort you can choose to put NaNs at the beginning just as easily: >>> sorted(l,key=lambda n: (n==n, n)) [nan, 1.0, 1.5, 1.7, 2.0] You want custom rules for sorting? You got 'em. ChrisA