On Thu, 7 Aug 2008, Dan Davison wrote:
On Wed, Aug 06, 2008 at 06:32:43PM -0400, Giuseppe Paleologo wrote:
I was posed the following problem/teaser:
given two matrices, come up with an "elegant" (=fast & short) function that
returns a matrix with all and only the non-duplicated columns of both
matrices; the column order does not matter. In essence, a matrix equivalent
of union(x,y), where x and y are vectors. I could not come with anything
nice. Any ideas?
union.matrices <- function(a, b) {
u <- cbind(a,b)
u[,!duplicated(u, MARGIN=2)]
}
?
Or just
union.matrices <- function(a, b) unique( cbind( a , b ), MARGIN=2 )
Chuck
(Obviously not attempting to deal with issues of identity of columns containing
real numbers)
Dan
Giuseppe
--
Giuseppe A. Paleologo :: Email: [EMAIL PROTECTED] :: AOL: gappy3000 ::
Skype :: gappy3000 :: Gtalk: paleologo :: Mobile: 917.331.3497
fact: 2^32,582,657-1 is a prime
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Charles C. Berry (858) 534-2098
Dept of Family/Preventive Medicine
E mailto:[EMAIL PROTECTED] UC San Diego
http://famprevmed.ucsd.edu/faculty/cberry/ La Jolla, San Diego 92093-0901
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