[R] colSums

[Marcel Wolbers]

>> 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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