[R] Loop elimination question
Prof Brian Ripley
ripley at stats.ox.ac.uk
Wed Nov 1 10:21:36 CET 2000
On Wed, 1 Nov 2000, Murray Jorgensen wrote:
> I want to make a vector built up from several parts. Each part consists of 3
> followed by a variable number of 4s. The number of 4s is given by a vector
> called dim, say
>
> dim <- c(3,1,4,1,5)
>
> From this I want to produce
>
> 3 4 4 4 3 4 3 4 4 4 4 3 4 3 4 4 4 4 4
>
> Now the following code seems to work
>
> type <- numeric(0)
> for (j in seq(along=dim)) {
> type <- c(type,3,rep(4,dim[j]))}
>
> and I won't really need it to work for very large dim vectors so you could say
> my problem is solved. I am wondering, though, if the loop can be eliminated.
Using rep:
rep(rep(c(3,4), length(dim)), as.vector(t(cbind(1, dim))))
for example.
--
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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