# Duplicity in Set

**URL:** <https://www.ruby-forum.com/t/duplicity-in-set/57483>\
**Category:** Ruby\
**Created:** [April 11, 2006, 12:30pm UTC](https://www.ruby-forum.com/t/duplicity-in-set/57483 "2006-04-11T12:30:39Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![Radek\_Skokan](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/278dde/32.png) [@Radek\_Skokan](https://www.ruby-forum.com/u/Radek_Skokan)\
**Post date:** [April 11, 2006, 12:30pm UTC](https://www.ruby-forum.com/t/duplicity-in-set/57483/1 "2006-04-11T12:30:39Z")

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Hello,

I have a Set which should contains elements of my object Component. The  
component class implements method hash. I’m gathering data, createing  
Componets from them and storing it into the Set. It’s a Set just to  
prevent  
duplicates. But finally the Set contains duplicate elemets – with the  
same  
hash value.

Few snippets from the code:

$components = Set.new # declaration of the Set variable  
… then some addings to $components …  
$components.each {|c| puts(c.name + ‘, class:’ + c.class.name + ‘,  
hash:’ +  
c.hash.to\_s)}

And it prints:

OR-copm2.2, class:Component, hash:304328379  
OR-copm2.2, class:Component, hash:304328379

The Component class is defined in this way:

Class Component  
attr\_reader :attributes, :name, :subcomponents  
attr\_writer :attributes # array of Attribute objects

```
def assembly?
    @subcomponents.length != 0
end

def object_id
    @name.object_id
end

def hash
    @name.hash
end

def initialize(name)
    @name = name
    @attributes = Hash.new
    @subcomponents = Array.new
end

```

end

What am I doing wrong?

Thanks,  
Radek

---

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**Author:** ![Radek\_Skokan](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/278dde/32.png) [@Radek\_Skokan](https://www.ruby-forum.com/u/Radek_Skokan)\
**Post date:** [April 11, 2006, 1:10pm UTC](https://www.ruby-forum.com/t/duplicity-in-set/57483/2 "2006-04-11T13:10:37Z")

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On Apr 11, 2006, at 12:28 PM, Radek Skokan wrote:

> I have a Set which should contains elements of my object Component.  
> The  
> component class implements method hash. I’m gathering data, createing  
> Componets from them and storing it into the Set. It’s a Set just to  
> prevent  
> duplicates. But finally the Set contains duplicate elemets – with  
> the same  
> hash value.

You must implement #eql? and #hash –

require ‘set’

class Component  
attr\_accessor :attributes  
attr\_reader :name, :subcomponents  
def initialize(name)  
@name = name  
@attributes = {}  
@subcomponents = []  
end  
def inspect() %{\<%s hash=%#x @name=%s\>} % [self.class.name,  
self.hash, @name.inspect] end  
def eql?(other) @name.eql?(other.name) end  
def hash() @name.hash end  
end

components = Set.new  
components \<\< Component.new(“foo”)  
components \<\< Component.new(“bar”)  
components \<\< Component.new(“foo”)  
components.each { |c| puts c.inspect }

– Daniel

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<div class="post-metadata">

**Author:** ![Radek\_Skokan](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/278dde/32.png) [@Radek\_Skokan](https://www.ruby-forum.com/u/Radek_Skokan)\
**Post date:** [April 11, 2006, 1:41pm UTC](https://www.ruby-forum.com/t/duplicity-in-set/57483/3 "2006-04-11T13:41:17Z")

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Thanks Daniel, I omitted the eql?. Now it works.  
Radek