R help - Jul 2001 - colSums

As best I understand it, colSums (and associated functions) in S+ 6 are
optimized functions (calling special C routines) for doing simple matrix
math. For example, it seems like (in S+):

all.equal(colSums(m), apply(m, 2, sum))

should be TRUE for any matrix m. It also seems like colSums (and its brethren)
are very fast.

My question: Are there equivalents to colSums in R?

Thanks,

Dave Kane
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>> My question: Are there equivalents to colSums in R?
I don't think there are functions for doing this, but you can speed 
up things a lot by using matrix operations instead of apply if
this is possible:
> x <- matrix(rnorm(1E5),ncol=100)
> system.time(tmp1 <- apply(x,2,sum))
[1] 0.04 0.01 0.05 0.00 0.00
> system.time(tmp2 <- c(rep(1,nrow(x))%*%x))
[1] 0.01 0.00 0.01 0.00 0.00
> all.equal(tmp1,tmp2)
[1] TRUE

Yours,
Marcel Wolbers

-- 
Marcel Wolbers, LEO C14, Seminar for Statistics, ETH Zurich
CH-8092 Zurich, Switzerland; phone: (01) 632 2252	
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