[R] Loop with variable index

[Ken Knoblauch]

 <Bill.Venables <at> csiro.au> writes:
> 
> y <- sort(rnorm(20))  # say...
> 
> m <- s <- numeric(19)
> 
> for(i in 2:20) {
> 	m[i-1] <- mean(y[1:i])
> 	s[i-1] <- sd(y[1:i])
> } 
> -----Original Message-----
> On Behalf Of cvandy
> Subject: [R] Loop with variable index
> I have a list of 20 values.  The first time through a loop I want to
> find the
> mean and stnd.dev. of the first two values; the second time through the
> loop I want to find the mean and stnd. dev. of  the first 3 values, etc.
> until  the last time through the loop I want to find the mean and stnd. dev. of
> all  20 values,  so I end up with 19 means and stnd. deviations.
> How would I construct such a loop?
> Thanks. 

Just for an alternative to some of the sapply solutions, 
the means can also be obtained with 

(cumsum(y)/(1:length(y)))[-1]

ken