From: "Simon Kröger" <SimonKroeger@...>
Date: 2005-12-14T05:03:42+09:00
Subject: Re: Array.invert

Christer Nilsson wrote:
> Kroeger, Simon (ext) wrote:
> 
>>Hi Christer,
>>
>>don't take this to serious:
>>
>>a = [[1,3],[1,4,5]]
>>p (0...a.size).zip(a).inject([]){|s, b| b[1].each{|i| (s[i] ||= []) <<
>>b[0]}; s}
>>
>>=> [nil, [0, 1], nil, [0], [1], [1]]
>>
>>cheers
>>
>>Simon
> 
> 
> Ruby is so fun, it's impossible to be serious :-)
> 
> a.invert works but not a.invert.invert
> 
> Can you fix that in your amazing oneliner ?
> Clue: nil.each is the bummer.
> 
> Christer

rofl!

i will give you two:

class Array
   def invert
     zip([*(0...size)]).inject([]){|s, b| (b.first || []).each{|i| (s[i] 
||= []) << b.last}; s}
   end
end

or (even worse):

class Array
   def invert
     Array.new(flatten.compact.max.succ){|i| 
zip([*(0...size)]).find_all{|b, j| b && b.include?(i)}.transpose[1]}
   end
end


cheers

Simon