From: Robert Dober <robert.dober@...>
Date: 2007-03-13T21:40:14+09:00
Subject: Re: non-destructive merging of hashes in array

On 3/13/07, Trans <transfire@gmail.com> wrote:
>
>
> On Mar 12, 10:01 pm, "Giles Bowkett" <gil...@gmail.com> wrote:
> > Hi, I have an array of hashes. The keys in the hashes represent the same things.
> >
> > eg:
> >
> > h1 = {:rabbits => 5}
> > h2 = {:rabbits => 10}
> >
> > bunnies = [h1, h2]
> >
> > I want to end up with this:
> >
> > {:rabbits => 15}
> >
> > It's a trivial task, but what's the quickest way to get there? I'm
> > certain it can be done on one line.
> >
> > I know there's a Hash#update, but it appears that it would just
> > replace the 10 with 5, or vice versa, rather than adding them up.
> >
> > This works, but it seems clunky:
> >
> > hashes.each do |h|
> >   h.each do |k, v|
> >     if new_hash[k]
> >       new_hash[k] += v
> >     else
> >       new_hash[k] = v
> >     end
> >   end
> > end
> >
> > It can be crammed all onto one line, too, but there must be a nicer way.
>
> (SORRY IF THIS GETS POSTED TWICE)
>
> The inject/merge solutions are good, but they are one trick ponies.
> How about something like:
>
>    OpenCollection[h1, h2].rabbits.sum
>
> It shouldn't be too hard to write:
>
>    require 'ostruct'
>
>    class OpenCollection
>      class << self ; alias :[] :new ; end
>      def initialize(*hashes)
>        @opens = hashes.collect { |h| OpenStruct.new(h) }
>      end
>
>      def method_missing(sym, *args)
>        @opens.collect{ |o| o.send(sym) }
>      end
>    end
>
> Actually, I'd use Facets OpenObject instead OpenStruct myself, but
> that's just me. You'll also need:
>
>   require 'facets/core/enumerable/sum'
>
> For fun, here's a one line version (more or less):
>
>    require 'facets/more/functor'
>
>    oc = Functor.new([h1,h2]){|s,m| m.map{|h| h[s]}}
>
>    oc.rabbits.sum
>
> T.
>
>
>
Tom Facet is a great thing and I do not fail to point to it regulary.
But sometimes I feel we have to flex our muscles in pure Ruby before
we shall use libraries, even excellent ones like Facets, just to
understand everything a little better.

This all does not mean that your post is not very valuable, I just
want to warn from the "Pull In A Library before Do Some Thinking"
approach.

i fear that this approach hurts the user as much as the library.

Cheers
Robert

-- 
You see things; and you say Why?
But I dream things that never were; and I say Why not?
-- George Bernard Shaw