From: Mike Steiner <mikejaysteiner@...>
Date: 2007-05-12T00:37:52+09:00
Subject: Re: how to remove dups from 2 lists?

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I'm looking for a function that will eliminate all matching items, like
canceling terms in a fraction. If the first list has 3 "a"s, and the second
list has 5 "a"s, then afterwards the first list should have 0 "a"s and the
second list should have 2 "a"s.

Mike Steiner

On 5/10/07, Rob Biedenharn <Rob@agileconsultingllc.com> wrote:
>
>
> On May 10, 2007, at 10:18 PM, Mike Steiner wrote:
>
> > I'm trying to write some code that removes all elements from 2
> > lists that
> > are in both lists. However, I don't want any duplicates from each list
> > deleted also (which is what the array "-" operator does). The code
> > I have
> > now doesn't handle restarting the current iteration for both loops
> > when a
> > match is found and deleted in both loops. Here's the code:
> >
> > def RemoveDupsFromLists ( list1 , list2 )
> >    list1.each_index do | i |
> >        list2.each_index do | j |
> >            if list1[i] == list2[j]
> >                list1.delete_at ( i )
> >                list2.delete_at ( j )
> >            end
> >        end
> >    end
> >    return [ list1 , list2 ]
> > end
> >
> > What's weird is that doing this is easy in C (my first language), but
> > difficult in Ruby. Everything else I've seen has been MUCH easier
> > in Ruby.
> >
> > Mike Steiner
>
> Having some examples might help, but is something like this what
> you're after?
>
> >> a = %w[ a a a b b c ]
> => ["a", "a", "a", "b", "b", "c"]
> >> b = %w[ b c c c d ]
> => ["b", "c", "c", "c", "d"]
> >> a + b
> => ["a", "a", "a", "b", "b", "c", "b", "c", "c", "c", "d"]
> >> a | b
> => ["a", "b", "c", "d"]
> >> a - b
> => ["a", "a", "a"]
> >> a & b
> => ["b", "c"]
> >> a - (a & b)
> => ["a", "a", "a"]
> >> b - (a & b)
> => ["d"]
>
> In particular, which do you expect from RemoveDupsFromLists( a, b )?
>
> What I have for the last two expressions above:
> => [ ["a", "a", "a"], ["d"] ]
>
> Or:
> => [ ["a", "a", "a", "b"], ["c", "c", "d"] ]
> because it works like canceling terms in a fraction:
>
>   ["a", "a", "a", "b", "b", "c"]
> -----------------------------------------------
>                       ["b", "c", "c", "c", "d"]
>
>
> Basically, write a test:
>
> require 'test/unit'
> class RemoveDupsTest < Test::Unit::TestCase
>    def test_simple
>      list1 =  ["a", "a", "a", "b", "b", "c"]
>      list2 =  ["b", "c", "c", "c", "d"]
>      expects = [ [__,__], [__,__] ] #<=== fill me it!
>      assert_equals expects, RemoveDupsFromLists(list1, list2)
>    end
> end
>
> Then you'll know what you want (and so will we!) and you'll be sure
> when you get it working.
>
> -Rob
>
> Rob Biedenharn          http://agileconsultingllc.com
> Rob@AgileConsultingLLC.com
>
>
>
>

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