Try using tabulate() instead of table(). E.g.,
compare your original
f0 <- function (x, u) {
tu <- table(u)
indices <- as.numeric(names(tu))
x[indices] <- x[indices] + tu
x
}
to
f1 <- function (x, u) {
x + tabulate(u, nbins = length(x))
}
I tried it for a 20-long x and 30-long u. f0 and f1
gave identical results. 10^5 iterations of f0 took
62 seconds, f1 1.72 seconds.
Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com
> -----Original Message-----
> From: r-help-boun...@r-project.org
> [mailto:r-help-boun...@r-project.org] On Behalf Of Eric Elguero
> Sent: Thursday, February 10, 2011 3:50 AM
> To: r-help@r-project.org
> Subject: [R] modifynig some elements of a vector
>
> He everybody,
>
> I want to add 1 to some elements of a vector:
>
> x is a vector
> u is a vector of idices, that is, integers
> assumed to be within the range 1..length(x)
> and I want to add 1 to the elements of x
> each time their index appears in u
>
> x[u]<-x[u]+1 works only when there are no
> duplicated values in u
>
> I found this solution:
>
> tu <- table(u)
> indices <- as.numeric(names(tu))
> x[indices] <- x[indices]+tu
>
> but it looks ugly to me and I would
> prefer to avoid calling the function 'table'
> since this is to be done millions of times
> as part of a simulation program.
>
> Eric Elguero
> Génétique & Adaptation des Plasmodium
> IRD
> Montpellier - FRance
>
> ______________________________________________
> R-help@r-project.org mailing list
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> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>
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