R help - Mar 2008 - Help on vectorizing

Dear R-helpers,
 
I have two problems that I don't know how to vectorize (but would like to
because my current solution is slow).
 
# 1.
#I have a vector x:
 
x <- c(3, 0, 1, 0, 2, 2, 2, 0, 4, 2)
 
#I want this translated into a new vector based on x,so that each element of x
#is the number of zeroes, followed by a 1. The new vector would look like:
 
#> r# [1] 0 0 0 1 1 0 1 1 0 0 1 0 0 1 0 0 1 1 0 0 0 0 1 0 0 1
 
# I only found a solution that loops, and it's a bit ugly:
r <- c()for(i in 1:length(x))r <- c(r, rep(0,pmax(0,x[i])),1)
 
 
# 2. 
# The other way around, so that we have the vector r, and want to find x.
# I have a (very) ugly solution:
chars <- paste(r,collapse="")zeros <-
strsplit(chars,"1")x <- nchar(zeros[[1]])
 
 
 
Thanks for your help!
 
Remko Duursma
	[[alternative HTML version deleted]]

Try this:

r <- unlist(sapply(x, function(x) c(rep(0, x), 1)))
x2 <- diff(c(0, which(r==1))) - 1
identical(x, x2)


On Sun, Mar 9, 2008 at 7:55 PM, remko duursma <remkoduursma at
hotmail.com> wrote:
>
> Dear R-helpers,
>
> I have two problems that I don't know how to vectorize (but would like
to because my current solution is slow).
>
> # 1.
> #I have a vector x:
>
> x <- c(3, 0, 1, 0, 2, 2, 2, 0, 4, 2)
>
> #I want this translated into a new vector based on x,so that each element
of x
> #is the number of zeroes, followed by a 1. The new vector would look like:
>
> #> r# [1] 0 0 0 1 1 0 1 1 0 0 1 0 0 1 0 0 1 1 0 0 0 0 1 0 0 1
>
> # I only found a solution that loops, and it's a bit ugly:
> r <- c()for(i in 1:length(x))r <- c(r, rep(0,pmax(0,x[i])),1)
>
>
> # 2.
> # The other way around, so that we have the vector r, and want to find x.
> # I have a (very) ugly solution:
> chars <- paste(r,collapse="")zeros <-
strsplit(chars,"1")x <- nchar(zeros[[1]])
>
>
>
> Thanks for your help!
>
> Remko Duursma
>        [[alternative HTML version deleted]]
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>