From: Orion Hunter <orion2480@...>
Date: 2003-06-10T04:47:59+09:00
Subject: Re: array.uniq does not use == ?

I believe that might do the trick, but it still seems like there should be a 
more elegant solution, for my particular problem.  Let me define my problem 
a little more to help clarify.

My Agent is an object I wish to use in a genetic algorithm.  Among other 
things, it has attributes chromosome and fitness.  I have "mixed in" the 
Comparable module and defined my <=> operator so I can sort my Agents based 
on their level of fitness.

However, I wish to grab "unique" agents based on their chromosomes as well.  
Now, technically, if an agent has the same chromosome as another, it will 
evaluate to the same fitness, but it is possible to have identicle fitness 
with different chromosomes.

So, among the attributes of my agent, I  wish to consider _only_ the 
chromosome when I look for uniqueness.  I don't need anything else.  So, 
basically, I was hoping to find an elegant "Ruby Way" style solution, where 
all I need to do is override the Array.uniq, or override the operator for 
which it derives its answer.  However, I cannot seem to figure out how 
exactly uniq is comparing objects.

And, actually, after taking a closer look at the solution you provided... 
I'm not too sure I see how would work.  Doesn't .inspect also return the 
Object.hash attribute of the object, which, unless defined otherwise, will 
be different for every object?  This would then make each object different, 
even if all the other attributes are the same.

Matt


>From: Mark Wilson <mwilson13@cox.net>
>Reply-To: ruby-talk@ruby-lang.org
>To: ruby-talk@ruby-lang.org (ruby-talk ML)
>Subject: Re: array.uniq does not use == ?
>Date: Tue, 10 Jun 2003 04:04:21 +0900
>
>
>On Monday, June 9, 2003, at 02:43 PM, Orion Hunter wrote:
>
>>I have a user defined object, Agent.  And I want to pass my Agents around 
>>in an Array.  I've "mixed-in" the  Comparable module, and defined <=> 
>>within the class for sorting purposes.   However, I _also_ want to be able 
>>to perform Array.uniq/Array.uniq! as well, having the decision on the 
>>"uniqueness" of the object derived from one particular attribute.
>>
>>[snip]
>
>I think the answer depends on the characteristics of the Agent object.
>
>Can you use a Set to hold your Agents? Depending on what the class of the 
>Agent is, each instance _might_ be treated as a separate object even if two 
>Agent objects have the same attributes (for example, this is true for Set  
>objects within a Set object). If this is the case, uniqueness on the basis 
>of attributes could be determined something like this:
>
># Deletes objects with duplicate attributes from the calling set. Used to 
>deal with a
># set object being able to contain two different set objects that have the 
>same elements.
>   def unique_attributes!
>     s = []
>     self.each { |e|
>       if s.include?(e.inspect)
>          self.delete(e)
>          s.push(e.inspect)
>       else
>         s.push(e.inspect)
>       end
>     }
>     self
>   end
>
>Note that you would need to separately define a unique_attributes to take 
>(set = self.dup) for the non-mutating version.
>
>This method could also be adapted if you have to use Arrays and can't use 
>Sets.
>
>Other additional set methods are at:
>
>http://www.rubygarden.org/ruby?AdditionalSetMethods
>
>Regards,
>
>Mark
>
>

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