From: Christer Nilsson <janchrister.nilsson@...>
Date: 2005-12-13T23:43:51+09:00
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

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