From: "Kroeger, Simon (ext)" <simon.kroeger.ext@...>
Date: 2005-12-14T01:11:23+09:00
Subject: Re: Array.invert

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 

> From: list-bounce@example.com 
> [mailto:list-bounce@example.com] On Behalf Of Christer Nilsson
> Sent: Tuesday, December 13, 2005 3:44 PM
> To: ruby-talk ML
> Subject: Array.invert
> 
> 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
> 
> require 'test/unit'
> class TestArray < Test::Unit::TestCase
>   def test_invert_1
>     a = [[1,3],[1,4,5]]
>     b = [nil,[0,1],nil,[0],[1],[1]]
>     assert_equal b,a.invert
>     assert_equal a,b.invert
>   end
> 
>   def test_invert_2
>     a = []
>     a << [3,9,13]         # 0
>     a << [3,11,14]        # 1
>     a << [3,14,15]        # 2
>     a << [4,1,4]          # 3
>     a << [4,8,9]          # 4
>     a << [5,0,1]          # 5
>     a << [6,6,7]          # 6
>     a << [14,2,6]         # 7
>     a << [10,5,8,12,15]   # 8
>     a << [10,10,11,12,13] # 9
>     a << [11,0,3,7,10]    # 10
>     a << [17,2,3,4,5]     # 11
> 
>     # behead...
>     c = a.map {|head, *tail| tail}
> 
>     b = []
>     b << [5,10] # 0
>     b << [3,5]  # 1
>     b << [7,11] # 2
>     b << [10,11]# 3
>     b << [3,11] # 4
>     b << [8,11] # 5
>     b << [6,7]  # 6
>     b << [6,10] # 7
>     b << [4,8]  # 8
>     b << [0,4]  # 9
>     b << [9,10] # 10
>     b << [1,9]  # 11
>     b << [8,9]  # 12
>     b << [0,9]  # 13
>     b << [1,2]  # 14
>     b << [2,8]  # 15
> 
>     assert_equal b,c.invert
>     assert_equal c,b.invert
> 
>   end
> end
> 
> Christer
> 
> -- 
> Posted via http://www.ruby-forum.com/.
> 
>