From: Markus Fischer <markus@...>
Date: 2011-06-09T23:03:20+09:00
Subject: [ruby-core:36889] [Ruby 1.9 - Feature #666] Enumerable::to_hash


Issue #666 has been updated by Markus Fischer.


Arnau Sanchez wrote:
> I don't know if it's polite to comment in old closed issues, excuse me if it's not.
> 
> I have to say that I wholeheartedly agree with Marc-Andre: the lack of Enumerable-to-Hash conversion is important; in my experience it's an extraordinarily common transformation. Let's see what people usually does (unaware of Facet's Enumerable#mash):
[...]
>  Hash[(1..3).map { |n| [n, n**2] }]
> 
> Not bad, but it's disappointing in a OOP language to "go back", you'd expect to write from left-to-right as usual and use a method. Moreover, it's less efficient because it needs an intermediate array to be built.
> 
> Somehow it's already defined:
> 
>  >> Hash[[1,2,3]]
>  => {}
> 
> Although it would be also ok to raise an exception (as Python does, for example). A mapping has been always represented by a collection of pairs (key, value), all languages with minimal functional capabilities (and Ruby has powerful ones) has such function/method transformation.

I was about to open a new feature request when I found this, unfortunately rejected, issue.

I'd also love to see Hash[] being available as Array#to_h too; it's just much more convenient. I recently had the urge to sort a hash and would could have been:

 some_hash.sort { |a,b| whatever_is_necessary }.to_h

had to be

 Hash[ some_hash.sort { |a,b| whatever_is_necessary } ]

- Markus

----------------------------------------
Feature #666: Enumerable::to_hash
http://redmine.ruby-lang.org/issues/666

Author: Marc-Andre Lafortune
Status: Rejected
Priority: Low
Assignee: Yukihiro Matsumoto
Category: 
Target version: 1.9.x


=begin
 There are many ways to obtain an array from enumerables (to_a, map, ...).
 There is no natural way to obtain a hash from an enumerable (except for Hash[some_array]).
 There is a Hash::to_a but no Array::to_hash.
 Here is what I would like:
 
 [[:hello, "world"], [:choice, [:red_pill, :blue_pill]]].to_hash ==> {:hello=>"world", :choice=>[:red_pill, :blue_pill]}
 (1..3).to_hash{|n| [n, n**2]} ==> {1 => 1, 2 ==> 4, 3 ==> 9}
 
 I propose to add the following Enumerable::to_hash :
 
 module Enumerable
   def to_hash
     result = {}
     self.each do |key, value|
       key, value = yield(key, value) if block_given?
       result[key] = value
     end
     result
   end
 end
 
 Since Hash::to_a returns an array of key-value pairs, I fell it's natural that a block to construct a Hash should return key-value pairs. 
 This definition has nice symmetric properties: for any Hash h, the following all return a copy of h.
 h.to_a.to_hash
 h.to_hash{|p| p}
 h.to_hash{|k,v| [k,v]}
 h.keys.zip(h.values).to_hash
 
 Thank you for your attention,
 
 Marc-Andre Lafortune
=end



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