[R] Overlapping assignment
Prof Brian Ripley
ripley at stats.ox.ac.uk
Tue Apr 25 08:31:01 CEST 2006
On Mon, 24 Apr 2006, Rob Steele wrote:
> Is it valid to assign a slice of an array or vector to an overlapping
> slice of the same object? R seems to do the right thing but I can't
> find anything where it promises to.
Yes. Remember R is a vector language, so it is not doing this
index-by-index. Also, what you are doing is
a <- `[<-`(a, 4:12, 1:9)
which should make this easier to understand: you get a new object, and you
don't expect
x <- x^2
to be a problem, do you?
>
> > a <- 1:12
> > a[4:12] <- a[1:9]
> > a
> [1] 1 2 3 1 2 3 4 5 6 7 8 9
>
> > b <- 1:12
> > b[1:9] <- b[4:12]
> > b
> [1] 4 5 6 7 8 9 10 11 12 10 11 12
>
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--
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 272866 (PA)
Oxford OX1 3TG, UK Fax: +44 1865 272595
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