Vectorization
system.time (
{
x.mx <- matrix (data = rand.nv, ncol = 2, nrow = len.n)
x1.nv <- apply (x.mx, 1, sum)
}
)
# user system elapsed
# 0.878 0.012 0.885
system.time (
{
x.mx <- matrix (data = rand.nv, ncol = 2, nrow = len.n)
x2.nv <- numeric ()
for (i in 1: 10^5)
{x2.nv[i] <- sum (x.mx[i, ])}
}
)
# user system elapsed
# 20.527 44.616 64.834
system.time (
{
x.mx <- matrix (data = rand.nv, ncol = 2, nrow = len.n)
i.ls <- as.list (1: len.n)
f.sum <- function (i.n, x.mx) {return (sum (x.mx[i.n, ]))}
x3.nv <- sapply (i.ls, f.sum, x.mx)
}
)
# user system elapsed
# 0.573 0.014 0.584