From: Stefano Crocco <stefano.crocco@...>
Date: 2007-10-29T17:53:05+09:00
Subject: Re: uniq on custom objects

Alle lunedě 29 ottobre 2007, daniel ĺkerud ha scritto:
> I cannot get uniq to work with an array of custom class-objects. It seems
> overriding hash is now enough. This is what I mean:
>
> class Obj
>   attr_reader :name, :number
>   def initialize(name, number)
>     @name = name
>     @number = number
>   end
>   def hash
>     return @name.hash
>   end
> end
>
> a = [Obj.new("apa", 1), Obj.new("apa", 2), Obj.new("smisk", 3)]
>
> => [#<Obj:0x31baca8 @number=1, @name="apa">, #<Obj:0x31bac80 @number=2,
> @name="apa">, #<Obj:0x31bac58 @number=3, @name="smisk">]
>
> a.uniq
>
> => [#<Obj:0x31baca8 @number=1, @name="apa">, #<Obj:0x31bac80 @number=2,
> @name="apa">, #<Obj:0x31bac58 @number=3, @name="smisk">]
>
> But i want only one instance of "apa", and it doesn't matter which. Is
> there something else I have to override?
>
> /D

I think you also need to override eql? so that it returns true if the two objects have the same name:

class Obj
  ...
  def eql? other
    @name.eql? other.name
  end

end

a = [Obj.new("apa", 1), Obj.new("apa", 2), Obj.new("smisk", 3)]

p a.uniq

=> [#<Obj:0xb7b7f75c @name="apa", @number=1>, #<Obj:0xb7b7f57c @name="smisk", @number=3>]

I hope this helps

Stefano