On Jun 15, 2010, at 1:12 AM, James McCreight wrote:
Hi R'ers-
I'll believe this can be done and that I'm just not clever enough.
I'm trying to do this in 2D, but i think we have the same problem in
1D.
#Assume you have some 1D time series
d<-rnorm(100)
#Say you want to get the average over intervals of different lengths
#like from time 10 to time 24 and time 51 to time 86
starts <- c(10,51)
ends <- c(24,86)
results <-c(NA,NA)
#then you'd typically loop
for (i in 1:2) { results[i] <- mean(d[starts[i]:ends[i]) }
can it be done without looping?
Depends on what you mean by "without looping":
> mapply(function(x,y,z){mean(z[x:y])} ,x=starts, y=ends,
MoreArgs=list(d))
[1] -0.219429514 -0.008565724
Probably no more, and quite possibly less, efficient than a for-loop.
Thanks in advance.
James
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