From: Daniel Harple <dharple@...>
Date: 2006-10-09T21:05:32+09:00
Subject: Re: Removing Duplicate Objects from Object List

On Oct 9, 2006, at 1:50 PM, Jeff Nyman wrote:

> The problem is that I need to go through each rule and check if it  
> is equal
> to *any* of the other rules that are in the list. If a duplicate is  
> found,
> one of the duplicate rules should be removed.


> class Rule
>   attr_accessor :point, :filter, :value
>
>   def initialize(point, filter, value)
>     @point = point
>     @filter = filter
>     @value = value
>   end
> end
>
> When a rule object needs to be added to the list, I do this:
>
> $ruleList.append(Rule.new(step.point2, rule, value))
>
> Does that give enough detail?
>
> In playing around a bit more, I tried this:
>
> rules_array = $ruleList.selection.collect { |rule| rule }
>
> Then I tried:
>
> rules_array.uniq!
>
> The problem is that this finds nothing as a duplicate. But that  
> makes sense
> (I think) because the object ID is probably being considered as  
> part of the
> test and those will, of course, not be duplicates.
>
> It sounds like you're saying it would be better to not use a Rule  
> class in
> the first place. Is that accurate?

You should implement #eql? and #hash methods on your class, and store  
all instances in a [Set](http://ruby-doc.org/stdlib/libdoc/set/rdoc/ 
classes/Set.html).

require "set"

class Rule
   attr_accessor :point, :filter, :value

   def initialize(point, filter, value)
     @point = point
     @filter = filter
     @value = value
   end

   def eql?(rule)
     rule.point.eql?(@point) &&
	  rule.filter.eql?(@filter) &&
	  rule.value.eql?(@value)
   end

   def hash
     @point.hash + @filter.hash + @value.hash
   end
end

rules_set = Set.new
rules_set << Rule.new(1, 1, 1)
rules_set << Rule.new(1, 1, 1) # duplicate rule
rules_set << Rule.new(1, 1, 2)
rules_set.size # => 2
rules_set # => #<Set: {#<Rule:0x89d78 @value=2, @filter=1, @point=1>,  
#<Rule:0x89db4 @value=1, @filter=1, @point=1>}>

-- Daniel