From: Sean O'Halpin <sean.ohalpin@...>
Date: 2009-02-02T02:31:45+09:00
Subject: Re: Array#to_h

On Sat, Jan 31, 2009 at 7:49 PM, Roger Pack <rogerpack2005@gmail.com> wrote:
> Not that I would find it useful at all, but is there is a Hash#to_a
> should there not be an Array#to_h?
> Thanks!
> -=r

It's useful in Ruby 1.8.x for those enumerable methods which return arrays, e..g

irb --> {:a => 1, :b => 2, :c => 3}.select{|k, v| v % 2 == 1 }
    ==> [[:c, 3], [:a, 1]]

irb --> {:a => 1, :b => 2, :c => 3}.select{|k, v| v % 2 == 1 }.to_hash
    ==> {:a=>1, :c=>3}

whereas in Ruby 1.9.x, select (map, etc.) return hashes:

irb(main):001:0> {:a => 1, :b => 2, :c => 3}.select{|k, v| v % 2 == 1 }
=> {:a=>1, :c=>3}

The problem is, as other posters have noted, that there is no 1-1
mapping between an array and a hash. Having said that, I've found the
following to be handy (mainly in restoring a hash after the 1.8.x
transformation to an array):

module ToHash
  if RUBY_VERSION =~ /^1.9/
    def to_hash
      Hash[*flatten(1)]
    end
  else
    def to_hash
      Hash[*(inject([]) {|arr, i| i.kind_of?(Array) ? arr.push(*i) :
arr.push(i) })]
    end
  end
end

used like this:

  b = [
     [:a, [[1, 2], [3, 4]]],
     [:b, 3],
     [:c, { :d => 4 }],
    ]

  p b.extend(ToHash).to_hash

Regards,
Sean