From: Michael Ulm <michael.ulm@...>
Date: 2005-12-14T00:47:13+09:00
Subject: Re: Array.invert

Christer Nilsson wrote:

> I would like to see invert "rubyfied".
> (Yes, I'm trying to get a grip of what this word means :-)
> 
> class Array
>   def invert
>     res=[]
>     for i in 0...self.size
>       if self[i] != nil then
>         for b in self[i]
>           res[b] = [] if res[b].nil?
>           res[b] << i
>         end
>       end
>     end
>     res
>   end
> end
>

I suggest

class Array
   def invert
     result = []
     each_with_index do |ary, idx|
       next if ary.nil?
       ary.each {|val| (result[val] ||= []).push(idx)}
     end
     result
   end
end

As a matter of taste, you may want to write the two middle
lines in just one line as

       ary.each {|val| (result[val] ||= []).push(idx)} unless ary.nil?

HTH,

Michael

-- 
Michael Ulm
R&D Team
ISIS Information Systems Austria
tel: +43 2236 27551-219, fax: +43 2236 21081
e-mail: michael.ulm@isis-papyrus.com
Visit our Website: www.isis-papyrus.com