Set-like collection in C#/.NET

Is there a collection among .NET collection that doesn't allow duplicates?
ArrayList is very suitable for what I need, except it allows duplicate values.
I've searched the System.Collections namespace but couldn't find anything alike.

Couldn't find one myself so knocked up a simple implementation of Set

Thank you Norfy, very nice implementation.
I was going to implement a set anyway,
just wanted to check if there's already an implementation among .NET's collections.

No problem, just thought I would save you some typing.

For that alone could you 'rate this post'? :)

I would like to, but...

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You must spread some Reputation around before giving it to Norfy again.

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Ah yes, multiple inheritance post ;)

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Originally Posted by Norfy

Ah yes, multiple inheritance post ;)

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Yes. :blush:

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Originally Posted by mehdi62b (Rating Comment)

I learnt this from you,didn't get why you used a hashtable while you set every key to null..wel we could also use an IList..

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Quite simply, the behaviour of the keys collection of a Hashtable is that of a set.
For small sets then an IList is ok but for larger sets a Hashtable is quicker.

there are some interesting collections that NHibernate uses...
the DLL is Iesi.Collections.
I don't know the licensing policy, but i think they're ok generally. :)

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Originally Posted by Norfy

For small sets then an IList is ok but for larger sets a Hashtable is quicker.

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we want to just look for in an collection and keys in hashtable are just an ICollection ...hastable is fast but when we give a key and want its item,well its time is O(1)
but when we want to get whether an item is included or not..
no difference between a hashtable(keys) and IList...(both of them are an ICollection)
both of them have O(n).

Sorry mehdi62b I couldn't follow your comment.

Whether you ask a Hashtable for a value or if it contains a key the access time is not linear O(n) , it uses hashing for both.

The keys are returned as an ICollection but are not implemented as such internally.

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Originally Posted by Norfy

Whether you ask a Hashtable for a value or if it contains a key the access time is not linear O(n) , it uses hashing for both.

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I meant when we ask a hashtable whetere it contains a key the time is not O(1)..I meant it doesn't use hashing...
and you tell it use hashing(how?) ..I don't know exactly..
no problem...should have a look at one of my book :wave:

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Originally Posted by mehdi62b

I meant it doesn't use hashing...and you tell it use hashing(how?) ..I don't know exactly.

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Have you checked out Reflector yet?

Nice tool, lets you browse the (decompiled) core .NET libraries.

I will check that link :thumb:

Hi Norfy,
thank you very much for that link..I didn't know it..its very usefull tool
and yes,you were right..

public virtual bool Contains(object item);Declaring Type:System.Collections.ArrayList

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public virtual bool Contains(object item)
{
        if (item == null)
        {
                        for (int num1 = 0; num1 < this._size; num1++)
                        {
                                if (this._items[num1] == null)
                                {
                                                return true;
                                }
                        }
                        return false;
        }
        for (int num2 = 0; num2 < this._size; num2++)
        {
                        if (item.Equals(this._items[num2]))
                        {
                                return true;
                        }
        }
        return false;
}

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and it clearly shows it has O(n)

and to be countinued...