Path: csiph.com!usenet.pasdenom.info!goblin1!goblin2!goblin.stu.neva.ru!newsfeed.xs4all.nl!newsfeed3.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 0.014 X-Spam-Evidence: '*H*': 0.97; '*S*': 0.00; 'element': 0.07; 'received:80.91': 0.09; 'received:80.91.229': 0.09; 'received:gmane.org': 0.09; 'received:list': 0.09; 'question.': 0.14; 'random': 0.14; '...,': 0.16; 'choice,': 0.16; 'fruit': 0.16; 'integer.': 0.16; 'message-id:@4ax.com': 0.16; 'received:80.91.229.3': 0.16; 'received:plane.gmane.org': 0.16; 'set,': 0.16; 'storing': 0.16; 'tuple': 0.16; 'weight,': 0.16; 'example': 0.22; '(by': 0.24; 'choices': 0.24; 'integer': 0.24; 'url:home': 0.24; 'regardless': 0.24; 'header:X-Complaints-To:1': 0.27; 'point': 0.28; 'appear': 0.29; 'sets': 0.30; 'sep': 0.31; 'this.': 0.32; 'beginning': 0.33; 'convert': 0.35; 'but': 0.35; '+0200,': 0.36; 'acceptable': 0.36; 'ordered': 0.36; 'charset:us- ascii': 0.36; 'should': 0.36; 'list': 0.37; 'received:76': 0.38; 'jason': 0.38; 'to:addr:python-list': 0.38; 'to:addr:python.org': 0.39; 'received:org': 0.40; 'above,': 0.60; 'range': 0.61; 'first': 0.61; 'pick': 0.64; 'sum': 0.64; 'total': 0.65; 'chance': 0.65; 'talking': 0.65; 'containing': 0.69; 'dict()': 0.84; 'pardon': 0.84; '2013': 0.98 X-Injected-Via-Gmane: http://gmane.org/ To: python-list@python.org From: Dennis Lee Bieber Subject: Re: Weighted choices Date: Sun, 08 Sep 2013 20:21:32 -0400 Organization: IISS Elusive Unicorn References: <522CB887.9090000@rece.vub.ac.be> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit X-Gmane-NNTP-Posting-Host: adsl-76-249-24-8.dsl.klmzmi.sbcglobal.net X-Newsreader: Forte Agent 6.00/32.1186 X-No-Archive: YES 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: 41 NNTP-Posting-Host: 2001:888:2000:d::a6 X-Trace: 1378686098 news.xs4all.nl 15868 [2001:888:2000:d::a6]:45771 X-Complaints-To: abuse@xs4all.nl Xref: csiph.com comp.lang.python:53850 On Sun, 08 Sep 2013 19:48:55 +0200, Antoon Pardon declaimed the following: >Op 08-09-13 04:12, Jason Friedman schreef: >> choices = dict() >> choices["apple"] = 10 >> choices["pear"] = 20 >> choices["banana"] = 15 >> choices["orange"] = 25 >> choices["kiwi"] = 30 >> >> I want to pick sets of fruit, three in a set, where the chance of >> selecting a given fruit is proportional to its weight. In the example >> above, pears should appear twice as often as apples and kiwis should >> appear twice as often as bananas. > >Just a small question. Is a set of three bananas an acceptable outcome? If we are talking probabilities, regardless of what the weighting is, it should be probable (if unlikely) to get three-of-a-kind. However, I would not use a dictionary for this. An ordered list should work better... for small samples a list containing repeats (by weight) of each choice, and then use a random integer whose range is 0..len(list)-1 would suffice. choices = ["apple", "apple", "apple", ..., "kiwi", "kiwi" ] For longer lists, storing a tuple with the accumulating weight, and scanning from the beginning choices = [(10, "Apple"), (10+20, "Pear"), (10+20+15, "Banana")... ] generate random integer in the range of the sum of the weights, and accept the last tuple whose first element is less than the integer. {Or convert the weights to floating point (by dividing each by the total sum), same concept but random number in range 0.0..1.0} -- Wulfraed Dennis Lee Bieber AF6VN wlfraed@ix.netcom.com HTTP://wlfraed.home.netcom.com/