From: daniel@...42.com Date: 2020-03-09T13:31:32+00:00 Subject: [ruby-core:97420] [Ruby master Feature#16665] Add an Array#except_index method Issue #16665 has been updated by Dan0042 (Daniel DeLorme). That implementation would return an empty array for `[true,nil,nil].except_index(0)` Probably something a bit more like this: ```ruby @@undef = Object.new #using Qundef in C def except_index(*indexes) result = dup indexes.each do |ind| if ind.is_a?(Range) ind.each{ |i| result[i] = @@undef } else result[ind] = @@undef end end result.reject!{ |e| e == @@undef } result end ``` It's fun enough to implement, but is there a real-world use for this? I can't think of one. Usually if you want to remove elements from a list you'd use `reject`; having a list of indexes as an intermediary step seems like quite an unusual situation to me. Just because there's a positive counterpart doesn't mean we need a negative counterpart "for the sake of consistency". ---------------------------------------- Feature #16665: Add an Array#except_index method https://bugs.ruby-lang.org/issues/16665#change-84553 * Author: alex_golubenko (Alex Golubenko) * Status: Open * Priority: Normal ---------------------------------------- The main idea is to implement a method that we can use to exclude elements from the array by their indices. For example: ``` ruby %w( a b c d e f).except_index(0, -1) => ["b", "c", "d", "e"] %w( a b c d e f g h ).except_index(0..1, 3, -2..-1) => ["c", "e", "f"] ``` I was meeting many questions on the StackOverflow about how to do such functionality also found many topics about it. So I think it might a helpful addition. I spent a few days finding the proper solution on Ruby that might be acceptable with integers and ranges(both positive and negative) and has good performance: ```ruby def except_index(*indexes) indexes.each_with_object(dup) do |ind, obj| ind.is_a?(Range) ? ind.each { |i| obj[i] = false } : obj[ind] = false end.select(&:itself) end ``` As you can see it's have not the best readability so I think it's a good point to add a built-in method on C. -- https://bugs.ruby-lang.org/ Unsubscribe: