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 3E03219E0025 for ; Wed, 16 Dec 2015 02:05:28 +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 564FAB5D8F0 for ; Wed, 16 Dec 2015 02:37:29 +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 51FDB18CC7D0 for ; Wed, 16 Dec 2015 02:37:29 +0900 (JST) Received: from [221.186.184.76] (localhost [IPv6:::1]) by neon.ruby-lang.org (Postfix) with ESMTP id 47DBA120493; Wed, 16 Dec 2015 02:37:27 +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 983CA120468 for ; Wed, 16 Dec 2015 02:37:23 +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=nGowgpbQH9lBKk0mirytzFsUpqI=; b=VmolQ7eph7ZA3vry2o CdubQFQ5goCmwxF+ZfDQLhUddlfkAyjbVMK5V+mp7xGljns+rkawu80A+fAEbtvy FTlSO9Xj+uqxFof4ZWfzSSg6GInHj85qIYQQIpooseQN6t8euFUBMTrAofSOJ+os ofub9P5aj0hP2Pv0roDFzl4C8= Received: by filter0525p1mdw1.sendgrid.net with SMTP id filter0525p1mdw1.1599.56704FC9E 2015-12-15 17:37:13.168438822 +0000 UTC Received: from herokuapp.com (ec2-54-162-155-175.compute-1.amazonaws.com [54.162.155.175]) by ismtpd0002p1iad1.sendgrid.net (SG) with ESMTP id dd_dMBp1TF-FQKnPG25AAg for ; Tue, 15 Dec 2015 17:37:13.193 +0000 (UTC) Date: Tue, 15 Dec 2015 17:37:13 +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: 46858 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/Ymy4QrNMhiuLXJG8OTL2vJD1yS5Kz4fnngOlhVMgF+SupyXf9lr4ax4xTs5cSC H18RTup1TZMNVJW0FzpW0u7hQwEuped8z356lgzfLz71LELWYEZaMc9IO+DPYn1nk7oi76hoGd/5Xw 6AQiBNgiWqhcFU51LI++nWkK8NERMgNd3HR4 X-ML-Name: ruby-core X-Mail-Count: 72151 Subject: [ruby-core:72151] [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. Daniel, thank you for your interesting observations. I too am fond of enumerators (`[true, false].cycle` being a fav), and I can see the advantages here. In my second example, for example, one could write `w1.chars.difference(w2.chars).none? #=> true`, avoiding the need for the construction of a temporary array. On the other hand, if the method were often used in conjunction with other `Array` methods, tacking on `to_a` may become tiresome. The last line of my first example would become `u - a.difference(u).to_a`, my third example would be `a.difference(b).to_a.concat(b.difference(a).to_a)` and your example would be `a.difference(b).to_a | b.difference(a).to_a`. ---------------------------------------- Feature #11815: Proposal for method `Array#difference` https://bugs.ruby-lang.org/issues/11815#change-55562 * 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 removes 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` 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 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 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/