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 6302D19E0025 for ; Tue, 15 Dec 2015 17:16:06 +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 4176AB5D8E4 for ; Tue, 15 Dec 2015 17:48:05 +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 D3B3E18CC7B6 for ; Tue, 15 Dec 2015 17:48:05 +0900 (JST) Received: from [221.186.184.76] (localhost [IPv6:::1]) by neon.ruby-lang.org (Postfix) with ESMTP id BB5651204C0; Tue, 15 Dec 2015 17:48:04 +0900 (JST) X-Original-To: ruby-core@ruby-lang.org Delivered-To: ruby-core@ruby-lang.org Received: from o10.shared.sendgrid.net (o10.shared.sendgrid.net [173.193.132.135]) by neon.ruby-lang.org (Postfix) with ESMTPS id 89B4D120492 for ; Tue, 15 Dec 2015 17:48:01 +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=GfpTLNMW1QK0LOxLWTYnkHrfs8Y=; b=QEZfygEeaalyWfEkVZ h2nN8IzzZyBcEGhxNzXEyPlzcKtUse6aFgERLAwHI+bvrqFO6/nqPjglvm0GyZLx RE6peK5Y1nydBSRdZa++QgNxIx6xbFej2iAy/nlpK5B26QpXxksO/iicJMIrSV3a zk/V2BYy4k3BvxvhmvS264Dr8= Received: by filter0554p1mdw1.sendgrid.net with SMTP id filter0554p1mdw1.22566.566FD3BE15 2015-12-15 08:47:58.571719297 +0000 UTC Received: from herokuapp.com (ec2-50-17-46-143.compute-1.amazonaws.com [50.17.46.143]) by ismtpd0001p1iad1.sendgrid.net (SG) with ESMTP id pLKlhJCjRBGBE4E2ZBAauQ for ; Tue, 15 Dec 2015 08:47:57.054 +0000 (UTC) Date: Tue, 15 Dec 2015 08:47:56 +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: quoted-printable X-Redmine-MailingListIntegration-Message-Ids: 46848 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/Ymy4QrNMhiuLXJG8OTL2vJD1yS5B0i/ssoobYlr1q/KYM98dAtLirgNj0eaveY AHLC+EpeBd4nIvW1JtsY4TBE7HYdggrIWKIlv24BP+YcgKzJwfVUNtXIEPUss/EiOzvqdLkAkxi9HJ DOICfheTcw01tl2r1Vjpl4zcgHA+jEp+WYtPBVI5HFDG7Qf6wf7uDlwimw== X-ML-Name: ruby-core X-Mail-Count: 72141 Subject: [ruby-core:72141] [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. Martin D=C3=BCrst wrote: > Then why don't you just provide pointers to those SO (StackOverflow?) que= stions, with explanations on how Array#difference would make things easier? Martin, see my [SO answer here](http://stackoverflow.com/questions/24987054= /how-to-select-unique-elements), which contains links to a number of questi= ons where I did use the method in my answer.=20 ---------------------------------------- Feature #11815: Proposal for method `Array#difference` https://bugs.ruby-lang.org/issues/11815#change-55551 * Author: Cary Swoveland * Status: Open * Priority: Normal * Assignee:=20 ---------------------------------------- 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 removes only one matching= element from the receiver. For example: a =3D [1,2,3,4,3,2,2,4] b =3D [2,3,4,4,4] a - b #=3D> [1] c =3D a.difference b #=3D> [1, 3, 2, 2]=20 As you see, `a` contains three `2`'s and `b` contains `1`, so the first `2`= in `a` has been removed from `a` in constructing `c`. When `b` contains as= least as many instances of an element as does `a`, `c` contains no instanc= es of that element.=20 It could be implemented as follows: class Array def difference(other) dup.tap do |cpy| other.each do |e| ndx =3D 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 unique elements* a =3D [1,3,2,4,3,4] u =3D a.uniq #=3D> [1, 2, 3, 4] u - a.difference(u) #=3D> [1, 2] *Determine if two words of the same size are anagrams of each other* w1, w2 =3D "stop", "pots" w1.chars.difference(w2.chars).empty? #=3D> true *Identify a maximal number of 1-1 matches between the elements of two array= s and return an array of all elements from both arrays that were not matche= d* a =3D [1, 2, 4, 2, 1, 7, 4, 2, 9]=20 b =3D [4, 7, 3, 2, 2, 7]=20 a.difference(b).concat(b.difference(a)) #=3D> [1, 1, 4, 2, 9, 3, 7]=20 =20=20 To remove elements from `a` starting at the end (rather the beginning) of `= a`: a =3D [1,2,3,4,3,2,2,4] b =3D [2,3,4,4,4] a.reverse.difference(b).reverse #=3D> [1,2,3,2] `Array#difference!` could be defined in the obvious way. --=20 https://bugs.ruby-lang.org/