From: "ara.t.howard" <ara.t.howard@...>
Date: 2009-03-30T01:15:35+09:00
Subject: Re: Is there an idiom for mass-populating Hash keys?


On Mar 29, 2009, at 10:05 AM, Shot (Piotr Szotkowski) wrote:

> Hello, good folk of ruby-talk.
>
> I was wondering whether there’s a Ruby
> idiom to mass-populate keys of a Hash.
>
> I’m coding a graph class supporting labeled vertices, and I want to
> represent this relationship as a @vertices Hash, with keys being the
> actual vertices and values being their labels – initially all nil:
>
> class Graph
>  def initialize enum
>    @vertices = {}
>    enum.each { |vertex| @vertices[vertex] = nil }
>  end
> end
>
> Is there a more elegant way to take an enum
> and turn it into nil-referencing Hash keys?

dunno if it's really better but this is one approach:

cfp:~ > cat a.rb

hash = {}

enum = ('a'..'z')

hash.update Hash[*enum.zip([])]

p hash
cfp:~ > ruby a.rb
{["e", nil]=>["f", nil], ["o", nil]=>["p", nil], ["y", nil]=>["z",  
nil], ["i", nil]=>["j", nil], ["s", nil]=>["t", nil], ["c",  
nil]=>["d", nil], ["m", nil]=>["n", nil], ["w", nil]=>["x", nil],  
["g", nil]=>["h", nil], ["q", nil]=>["r", nil], ["a", nil]=>["b",  
nil], ["k", nil]=>["l", nil], ["u", nil]=>["v", nil]}




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