From: sawadatsuyoshi@...
Date: 2014-03-18T18:27:18+00:00
Subject: [ruby-core:61578] [ruby-trunk - Feature #5663] Combined map/select	method

Issue #5663 has been updated by Tsuyoshi Sawada.


I came to think that, if this feature is to be added, then are other methods to be considered: `flat_map` and `to_h`. I think it should be either the case that the corresponding feature added to all of these methods, or none.

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Feature #5663: Combined map/select method
https://bugs.ruby-lang.org/issues/5663#change-45861

* Author: Yehuda Katz
* Status: Assigned
* Priority: Normal
* Assignee: Yukihiro Matsumoto
* Category: lib
* Target version: next minor
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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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