[R] Union of columns of two matrices

Johnson, Eric A. (Seattle) Eric.Johnson10 at va.gov
Thu Aug 7 01:42:28 CEST 2008

If a and b are your matrices of common row length, unique() can solve

unique(cbind(a,b), MARGIN=2)


-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org]
On Behalf Of Giuseppe Paleologo
Sent: Wednesday, August 06, 2008 3:33 PM
To: r-help at r-project.org
Subject: [R] Union of columns of two matrices

I was posed the following problem/teaser:

given two matrices, come up with an "elegant" (=fast & short) function
returns a matrix with all and only the non-duplicated columns of both
matrices; the column order does not matter. In essence, a matrix
of union(x,y), where x and y are vectors. I could not come with anything
nice. Any ideas?


Giuseppe A. Paleologo :: Email: paleologo at gmail.com :: AOL: gappy3000 ::
Skype :: gappy3000 :: Gtalk: paleologo :: Mobile: 917.331.3497
fact: 2^32,582,657-1 is a prime

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