Surprisingly Slow Standard Deviation in R

Question

I am calculating standard deviations on an expanding window where at each point I recalculate the standard deviation. This seems like a fairly straightforward thing to do t

Answer 1

Edited to fix some typos, sorry.

This takes ~1.3 seconds on my machine:

t0 <- proc.time()[[3]]
x <- rnorm(8000)
z <- sapply(1000:8000,function(y){sd(x[seq_len(y)])})
print(proc.time()[[3]]- t0)

and I'd be willing to bet there are even faster ways of doing this. Avoid explicit for loops!