adding unordered pairs without duplicates

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bluedoze@yahoo.com - 27 Jun 2005 14:27 GMT

Hello,

I want to construct a list of pairs without dupliactes, not the key
value pairs, I just want to ensure that the pair (not ordered) is not
dupliacted in the list.

for example

method input: (3, 4), (5, 6), (4, 3), (6, 5)

method output: (3, 4), (5, 6).

I can do this manually, but is there any utility in the java language
itself ?

Bluedoze

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Ingo R. Homann - 27 Jun 2005 15:02 GMT

Hi bluedoze,

> Hello,
>
[quoted text clipped - 12 lines]
>
> Bluedoze

I would use a normal (Hash)Set and a class "UnorderedPair" that
overrides equals and hashCode in the desired manner. Perhaps, it's
useful to store the two values as a "min" and a "max".

Hth,
Ingo

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bluedoze@yahoo.com - 27 Jun 2005 15:11 GMT

it's actually not numbers, so I cannot use min and max.

any way thanks for the replies.

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Ingo R. Homann - 27 Jun 2005 15:43 GMT

Hi,

> it's actually not numbers, so I cannot use min and max.
>
> any way thanks for the replies.

Well, it must not be numbers to use min and max. That's also possible
for Strings, for example, indeed for all classes that implement Comparable.

Even, if the 'values' do not implement Comparable, it should be possible
to write a proper Pair-class.

Ciao,
Ingo

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Daniel Dyer - 27 Jun 2005 15:03 GMT

> Hello,
>
[quoted text clipped - 10 lines]
> I can do this manually, but is there any utility in the java language
> itself ?

If you use a collection that does not allow duplicates (such as a HashSet,
TreeSet or other Set implementation) then, given an appropriate
implementation of the equals() method (in your Pair class), any duplicates
will be discarded by the collection when you add them.

Beware, this is one of those situations where you really do need to
over-ride hashcode() when you override equals().

Dan.

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Daniel Dyer
http://www.footballpredictions.net

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adding unordered pairs without duplicates

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