From: Nobuyoshi Nakada <nobu@...>
Date: 2011-11-24T16:12:18+09:00
Subject: [ruby-core:41279] [ruby-trunk - Feature #5663] Combined map/select method


Issue #5663 has been updated by Nobuyoshi Nakada.

Category set to lib
Target version set to 2.0.0

=begin
What about:
  (1..10).grep(->(i){i.even?}){|i|i+1}
or
  (1..10).grep(:even?.to_proc){|i|i+1}
=end

----------------------------------------
Feature #5663: Combined map/select method
http://redmine.ruby-lang.org/issues/5663

Author: Yehuda Katz
Status: Open
Priority: Normal
Assignee: 
Category: lib
Target version: 2.0.0


It is pretty common to want to map over an Enumerable, but only include the elements that match a particular filter. A common idiom is:

enum.map { |i| i + 1 if i.even? }.compact

It is of course also possible to do this with two calls:

enum.select { |i| i.even? }.map { |i| i + 1 }

Both cases are clumsy and require two iterations through the loop. I'd like to propose a combined method:

enum.map_select { |i| i + 1 if i.even? }

The only caveat is that it would be impossible to intentionally return nil here; suggestions welcome. The naming is also a strawman; feel free to propose something better.


-- 
http://redmine.ruby-lang.org