[ruby-talk:16774] Re: uniq and "equivalence"

On Sat, 23 Jun 2001, ts wrote:

> >>>>> "H" == Hugh Sasse Staff Elec Eng <[e-mail]> writes:
> 
> >> Array#uniq make first an hash, then delete the elements.
> 
> H> is that Object#hash() or Hash.new()?  
> 
>   Hash::new

Ok, I see which elements can be deleted now... 
> 
> H>    Object#hash must return a fixnum such that
> H>    a.eql?(b) means a.hash = b.hash.  That is a pretty tall
> H>    order for arrays of floats.  Has anyone any suggestions
> H>    on how to proceed?
> 
>  Define a #hash method for your class Trapezoidal_fitness, actually because
>  it's not defined it use the default #hash function which is the id of the
>  object.

That's what I don't want, but how can one map a 4-D set
of floats on to Fixnums?  Maybe I should redefine uniq:

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

class Array
    def uniq
        finished = false
        other = self.dup
        while !finished
            finished = true
            other.each {
                |val|
                left  = self.index(val) 
                right = self.rindex(val)
                next if left == right
	        finished = false
                while right != left
                    self.delete_at(right)
		    right = self.rindex(val)
                end
                retry # restart the each...
            }
        end
        self
    end
end

class Wotsit
    attr_reader :a, :b
    def initialize(x,y)
        @a,@b = x, y
    end

    def ==(other)
       @a == other.a && @b == other.b 
    end
end

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

    class  Testing_Array < RUNIT::TestCase
        def test_feature1
            thing1 = Wotsit.new(1,2)
            thing2 = Wotsit.new(1,2)
            thing3 = Wotsit.new(2,2)
            thing4 = Wotsit.new(2,2)
            thing5 = Wotsit.new(2,2)
            mine = [thing1,thing2,thing3,thing3,thing3,
                    thing4,thing5,thing2,thing3,thing5]
            expected = [thing1,thing3]
	    assert_equal(expected, mine.uniq)
        end
    end

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

which gives

uniq_tmp.rb:4: warning: discarding old uniq
/usr/local/lib/ruby/site_ruby/1.6/runit/assert.rb:146: warning: concat (...) interpreted as method call
/usr/local/lib/ruby/site_ruby/1.6/runit/assert.rb:158: warning: concat (...) interpreted as method call

Testing_Array#test_feature1 .
Time: 0.001764
OK (1/1 tests  1 asserts)

Caffeine underflow: Maybe I don't need the retry after
messing up all the indices by deletion(s).
> 
> 
> Guy Decoux
> 
	Hugh