From: Trans <transfire@...>
Date: 2007-07-13T12:13:07+09:00
Subject: Re: Returning part of a hash



On Jul 12, 3:24 pm, Stefan Rusterholz <apei...@gmx.net> wrote:
> Trans wrote:
> >     def &(other)
> >       case other
> >       when Array
> >         k = (keys & other)
> >         Hash[*(k.zip(values_at(*k)).flatten)]
> >       else
> >         Hash.new[*(to_a & other.to_a).flatten]
> >       end
> >     end
>
> >   end
>
> > T.
>
> > ---
> >http://facets.rubyforge.org
>
> Hash[*something.flatten] will destroy any nested arrays (and if you're
> so unlucky to get an even amount of elements, it won't even raise).

Ah, nice catch thanks. I fixed it. But in the process, well, I just
have to get this off my chest....

Arrggghh!!!! Where's flatten(x)!? I know David Black asked for that
like YEARS AND YEARS ago and we still we don't have it? Come on!
Please, please put it in 1.9. I even wrote the C code myself two years
ago. I'll post it up on ruby-core. Okay? Okay?

Okay. Sorry for the digression... In any case, I worked around:

    def &(other)
      case other
      when Array
        k = (keys & other)
        Hash[*(k.zip(values_at(*k)).flatten)]
      else
        r = (to_a & other.to_a).inject([]) do |a, kv|
          a.concat kv; a
        end
        Hash[*r]
      end
    end

Better? That last version had a bug anyway --Hash.new[] should have
been Hash[].

Thanks Stefan,
T.