[R] Selecting transitive couples

[Agustin Lobo]

Dear list,

I'm trying to improve the following process:

Let pairs be a 2 col matrix of integers such as:

2 5
3 6
4 56
5 2
6 8
7 56
8 6
etc.

My goal is to select the transitive pairs, i.e., in
the above example:

2 5 (because there is 5 2 as well)
6 8 (because there is 8 6 as well)

The task is simple with a for loop, but
can anybody suggest a "genuine R" solution?
(That is, a vectorised operation).

Note that, in practice, matrix pairs
can have ~60000 rows.

Thanks

Agus

Dr. Agustin Lobo
Instituto de Ciencias de la Tierra (CSIC)
Lluis Sole Sabaris s/n
08028 Barcelona SPAIN
tel 34 93409 5410
fax 34 93411 0012
alobo at ija.csic.es


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