From: Hugh Sasse Staff Elec Eng <hgs@...>
Date: 2001-06-21T23:41:27+09:00
Subject: [ruby-talk:16706] Re: bag difference

On Thu, 21 Jun 2001, HarryO wrote:

> In article <p86Y6.80058$Ne5.3134820@e420r-sjo3.usenetserver.com>, "Niklas
> Frykholm" <niklas@kagi.com> wrote:
> 
> 
> 
> I plan to read this carefully when I have time, but here's what I came up
> with.  It's slightly more verbose, but I think an Array#delete_first()
> would be useful, which is a bonus.  How efficient it is depends on how
> efficient Array#index and Array#delete_at are, but I would guess they're
> very simple.
> 
> class Array
>  
>     def delete_first(x)
>  
>         if (i = self.index(x))
>             self.delete_at(i)
>         end
>  
>     end
>  
>     def bag_minus(other)
>  
>         difference = Array.new
>         unwanted  = other.clone
>  
>         self.each do |x|
>             if !unwanted.delete_first(x)
>                 difference.push(x)
>             end
>         end
>  
>         return difference
>     end
>  
> end
>  
> a = [0,0,1,1,1,2,2,3,3,3,3,4,4,5,5,6]
> b = [1,2,3,3,4]
>  
> puts "#{a}.bag_minus(#{b}) = #{a.bag_minus(b)}" # -->
> [0,0,1,1,2,3,3,4,5,5,6]
> 

Thank you.  I was a bit confused by the other solution too, but it seemed
to rely on going through the array more than once.  Anyway, I 
settled on this:


#!/usr/local/bin/ruby -w

class Array
   def bag_subtract!(other)
      other.each {
          |value|
          i = index(value)
          delete_at(i) if i
      }
      self
   end
end

if __FILE__ == $0
    require "runit/testcase"
    require 'runit/cui/testrunner'
    require 'runit/testsuite'

    class  Testing_class < RUNIT::TestCase
        def test_feature1
            mine = [1,1,2,3,3,3,4,4,4,5]
            other = [1,2,3,4,4,6]
            assert_equal([1,3,3,4,5],mine.bag_subtract!(other))
            # ... etc
        end
        #...
    end

    RUNIT::CUI::TestRunner.run(Testing_class.suite)
end

	Thank you all,
	Hugh