From: Daniel N <has.sox@...>
Date: 2007-03-28T10:13:07+09:00
Subject: Re: String Intersection. A better way

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On 3/28/07, Rob Biedenharn <Rob@agileconsultingllc.com> wrote:
>
> On Mar 27, 2007, at 8:13 PM, Timothy Hunter wrote:
> > Daniel N wrote:
> >> Hi all,
> >>
> >> I have an issue with strings.  I want the intesection of two
> >> strings but I'm
> >> not sure how to go about it.  I have two cases.
> >>
> >> Case 1:
> >> String 1 has the tail end intersecting with the start of string
> >> 2..  eg:
> >>
> >> String 1: The quick brown fox jumped over the lazy dog.
> >> String 2: fox jumped over the lazy dog.  And in other news bla bla
> >> bla
> >>
> >> The problem is I don't know how much is intersecting.
> >> What I've done is to take string 1 and say psudo code
> >>
> >> until match found
> >>   string2 =~ /^(value of string1)/
> >>   if match found set flag
> >>   else delete first char of string1
> >> loop again
> >>
> >> What is a better way to do this?
> >>
> >> Case 2:
> >>
> >> The start of String1 intersects with the end of string2  eg:
> >>
> >> String1:   And here we are with another string.
> >> String2:   bla bla bla.   And here we are
> >>
> >> I don't really know about this one yet...  I haven't gotten to it.
> >>
> >> Can anyone pls suggest what I might do?
> >>
> >> Thanx
> >> Daniel
> >>
> > Take a look at the MatchData class, particularly the #begin and
> > #offset methods.
> >
>
> What you might do is take a TDD approach (Test Driven Development)...
>
> Change the method body until the tests pass and you're all set!  Of
> course, seeing the tests might help you solidify what you expect the
> behavior to be.
>
> class String
>    # intersection of self and other
>    def &(other)
>      ''
>    end
> end
>
> if __FILE__ == $0
>    require 'test/unit'
>    class StringIntersectionTest < Test::Unit::TestCase
>      def setup
>        @empty = ''
>      end
>
>      def test_empty_string
>        assert_equal @empty, @empty & @empty, "empty with empty"
>        assert_equal @empty, 'not' & @empty,  "non-empty with empty"
>        assert_equal @empty, @empty & 'not',  "empty with non-empty"
>      end
>
>      def test_equal_strings
>        s = "Some long string that I'm ready to take to the intersection"
>        assert_equal s, s & s, "string with self"
>      end
>
>      def test_prefix
>        assert_equal 'f', 'f' & 'fr', 'single char string as prefix of
> other'
>        assert_equal 'f', 'fr' & 'f', 'other is single char prefix of
> string'
>        assert_equal 'fred', 'fred' & 'fredrick', 'multi-char string
> as suffix of other'
>        assert_equal 'fred', 'fredrick' & 'fred', 'other is multi-char
> suffix of string'
>      end
>
>      def test_suffix
>        assert_equal 'r', 'r' & 'fr', 'single char string as suffix of
> other'
>        assert_equal 'r', 'fr' & 'r', 'other is single char suffix of
> string'
>        assert_equal 'rick', 'rick' & 'fredrick', 'multi-char string
> as suffix of other'
>        assert_equal 'rick', 'fredrick' & 'rick', 'other is multi-char
> suffix of string'
>      end
>
>      def test_other_intersections
>        assert_equal 'site', 'new web site' & 'site-wide policy'
>      end
>
>      def test_other_empty_intersections
>        assert_equal @empty, 'fred' & 'ethel'
>        assert_equal @empty, 'The quick brown fox jumps over the lazy
> dog.' & 'The lazy dog lies under the jumping fox.'
>        assert_equal @empty, 'Blah, Blah, blah' & 'yada, yada, yada'
>      end
>    end
> end


Whoa... Thanx for the tests Rob.

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