From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Original-To: poffice@blade.nagaokaut.ac.jp Delivered-To: poffice@blade.nagaokaut.ac.jp Received: from kankan.nagaokaut.ac.jp (kankan.nagaokaut.ac.jp [133.44.2.24]) by blade.nagaokaut.ac.jp (Postfix) with ESMTP id 4599F19E002F for ; Mon, 14 Dec 2015 18:06:22 +0900 (JST) Received: from voscc.nagaokaut.ac.jp (voscc.nagaokaut.ac.jp [133.44.1.100]) by kankan.nagaokaut.ac.jp (Postfix) with ESMTP id 54BF9B5D8C1 for ; Mon, 14 Dec 2015 18:38:18 +0900 (JST) Received: from neon.ruby-lang.org (neon.ruby-lang.org [221.186.184.75]) by voscc.nagaokaut.ac.jp (Postfix) with ESMTP id D733C18CC7D0 for ; Mon, 14 Dec 2015 18:38:18 +0900 (JST) Received: from [221.186.184.76] (localhost [IPv6:::1]) by neon.ruby-lang.org (Postfix) with ESMTP id 4AFCE1204AC; Mon, 14 Dec 2015 18:38:17 +0900 (JST) X-Original-To: ruby-core@ruby-lang.org Delivered-To: ruby-core@ruby-lang.org Received: from o2.heroku.sendgrid.net (o2.heroku.sendgrid.net [67.228.50.55]) by neon.ruby-lang.org (Postfix) with ESMTPS id 3B5341204C1 for ; Mon, 14 Dec 2015 18:38:13 +0900 (JST) DKIM-Signature: v=1; a=rsa-sha1; c=relaxed; d=sendgrid.me; h=from:to:references:subject:mime-version:content-type:content-transfer-encoding:list-id; s=smtpapi; bh=AnyyjW4cThcWrTE/KUndFqmFUvM=; b=DYX0DtfToAiwTXKVq5 eaJeznShpYYZRakW/wvEHTn2V1gXyW2QSu6cVn6NonoYorNmQYl3WKJcrqxEt7DG AegezRJYfNFDLMlkkW0PKXKs/9BTc0fVJImORe96MkrhMFtj0WpHA5tmrMZTfONB 3/tct5TWntUdA0k7iFBQNVwPQ= Received: by filter0432p1mdw1.sendgrid.net with SMTP id filter0432p1mdw1.5527.566E8E0138 2015-12-14 09:38:09.603955449 +0000 UTC Received: from herokuapp.com (ec2-54-224-27-90.compute-1.amazonaws.com [54.224.27.90]) by ismtpd0001p1iad1.sendgrid.net (SG) with ESMTP id dS1gHs4JT9Cj4Lni4ziOwQ for ; Mon, 14 Dec 2015 09:38:09.491 +0000 (UTC) Date: Mon, 14 Dec 2015 09:38:09 +0000 From: cary@swoveland.com To: ruby-core@ruby-lang.org Message-ID: References: Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Redmine-MailingListIntegration-Message-Ids: 46820 X-Redmine-Project: ruby-trunk X-Redmine-Issue-Id: 11815 X-Redmine-Issue-Author: CaryInVictoria X-Redmine-Sender: CaryInVictoria X-Mailer: Redmine X-Redmine-Host: bugs.ruby-lang.org X-Redmine-Site: Ruby Issue Tracking System X-Auto-Response-Suppress: All Auto-Submitted: auto-generated X-SG-EID: ync6xU2WACa70kv/Ymy4QrNMhiuLXJG8OTL2vJD1yS4L0g3d6WPmMrq1YyXPQST7vVllSxxtEKJtLO 1AZ0ogWskT71Qld1MBRTZw3Smrr/lwznxtX5PTsRiy8QgmjFsgLNeKodEPul1wdVKsBSvmdXuBIAj7 tszM8dxXEXQaMQg7VovnpLucHNcvmYH0Bu3QiGiK7kZBwAPN2qWSEg2+aA== X-ML-Name: ruby-core X-Mail-Count: 72111 Subject: [ruby-core:72111] [Ruby trunk - Feature #11815] Proposal for method `Array#difference` X-BeenThere: ruby-core@ruby-lang.org X-Mailman-Version: 2.1.15 Precedence: list Reply-To: Ruby developers List-Id: Ruby developers List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Errors-To: ruby-core-bounces@ruby-lang.org Sender: "ruby-core" Issue #11815 has been updated by Cary Swoveland. "*Identify an array's non-unique elements*" should be "*Identify an array's unique elements*". ---------------------------------------- Feature #11815: Proposal for method `Array#difference` https://bugs.ruby-lang.org/issues/11815#change-55526 * Author: Cary Swoveland * Status: Open * Priority: Normal * Assignee: ---------------------------------------- I propose that a method `Array#difference` be added to the Ruby core. It is similar to [Array#-](http://ruby-doc.org/core-2.2.0/Array.html#method-i-2D) but for each element of the (array) argument it remove only one matching element from the receiver. For example: a = [1,2,3,4,3,2,2,4] b = [2,3,4,4,4] a - b #=> [1] c = a.difference b #=> [1, 3, 2, 2] As you see, `a` contains three `2`'s and `b` `1`, so the first `3-1 #=> 2` `2`'s in `a` have been removed from `a` in constructing `c`. When `b` contains as least as many instances of an element as does `a`, `c` contains no instances of that element. It could be implemented as follows: class Array def difference(other) dup.tap do |cpy| other.each do |e| ndx = cpy.index(e) cpy.delete_at(ndx) if ndx end end end end Here are a few examples of its use: *Identify an array's non-unique elements* a = [1,3,2,4,3,4] u = a.uniq #=> [1, 2, 3, 4] u - a.difference(u) #=> [1, 2] *Determine if two words of the same size are anagrams of each other* w1, w2 = "stop", "pots" w1.chars.difference(w2.chars).empty? #=> true *Identify a maximal number of 1-1 matches between the elements of two arrays and return an array of all elements from both arrays that were not matched* a = [1, 2, 4, 2, 1, 7, 4, 2, 9] b = [4, 7, 3, 2, 2, 7] a.difference(b).concat(b.difference(a)) # => [1, 1, 4, 2, 9, 3, 7] To remove elements from `a` starting at the end (rather the beginning) of `a`: a = [1,2,3,4,3,2,2,4] b = [2,3,4,4,4] a.reverse.difference(b).reverse #=> [1,2,3,2] `Array#difference!` could be defined in the obvious way. -- https://bugs.ruby-lang.org/