[R] How to?
Prof Brian D Ripley
ripley at stats.ox.ac.uk
Fri Aug 25 19:09:44 CEST 2000
On Fri, 25 Aug 2000, Yves Gauvreau wrote:
> I tried the function you proposed and I get an error:
> Error in substr(x, as.integer(start), as.integer(stop)) :
> invalid argument in substr()
> I must admit I don't understand the use of substr() in this case, x being a
> numerical vector. I understand that your using it to provide FUN with its
> argument i.e. the window of data. I'm using R1.1 on NT does this mean it
> could work width with the newer version?
I said `something like' (that's code for `I haven't tried this'), and I
mis-remembered what substr does. Try this:
mywinfun <- function(x, width, FUN, ...)
n <- length(x)
A <- rep(x, length=width*(n+1))
dim(A) <- c(n+1, width)
sapply(split(A, row(A)), FUN, ...)[1:(n-width)]
It's more efficient than embed, and more efficient that apply(A, 1,...)
in this case. But there are limits to how efficient interpreted R code
gets in such problems.
Brian D. Ripley, ripley at stats.ox.ac.uk
Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/
University of Oxford, Tel: +44 1865 272861 (self)
1 South Parks Road, +44 1865 272860 (secr)
Oxford OX1 3TG, UK Fax: +44 1865 272595
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