From: Thomas Sawyer <transfire@...>
Date: 2012-02-14T05:48:06+09:00
Subject: [ruby-core:42571] [ruby-trunk - Feature #5663] Combined map/select method


Issue #5663 has been updated by Thomas Sawyer.


@rodrigo

Your right, I could have used nil, so my example wasn't a particularly good one for what I was trying to demonstrate. Here's a better demonstration:

  [0,1,-1,2].compact_map(foo) do |e|
    case e
    when  0 then nil
    when  1 then true
    when -1 then false
    else         foo
    end
  end
  #=> [nil,true,false]


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Feature #5663: Combined map/select method
https://bugs.ruby-lang.org/issues/5663

Author: Yehuda Katz
Status: Assigned
Priority: Normal
Assignee: Yukihiro Matsumoto
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.


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