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Re: Array.invert

Kroeger, Simon (ext)

12/13/2005 4:11:00 PM

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-....
>
>


5 Answers

Christer Nilsson

12/13/2005 4:57:00 PM

0

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

Is it possible to wrap this in a method ?
I tried but I get a nil.each error.

Christer

--
Posted via http://www.ruby-....

Christer Nilsson

12/13/2005 5:11:00 PM

0

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


--
Posted via http://www.ruby-....

Simon Kröger

12/13/2005 8:04:00 PM

0

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

dblack

12/13/2005 8:32:00 PM

0

Christer Nilsson

12/13/2005 11:35:00 PM

0

Simon wrote:
>
> 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

I didn't know invert was so complex that ten keywords were needed!
The more keywords, the more cycles.
My original old fashioned fortran style polyliner is still quickest :-)

Christer

--
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