[R] subscripts in lists
Prof Brian Ripley
ripley at stats.ox.ac.uk
Tue Aug 12 10:19:39 CEST 2003
On Tue, 12 Aug 2003, Peter Wolf wrote:
> What about ...
> > unlist(lis)[which(unlist(lis)=="next")+1]
>  "want1" "want2"
> ... to avoid the loop in sapply?
That has a loop in each unlist, of course. (A slicker version of that
solution was posted earlier by Richard.)
Note that you have to loop over the list elements to do this: both sapply
(really lapply) and unlist do that in C code. It's not even clear to me
that it is worth avoiding looping in R code: for() loops in R are pretty
efficient, and the collective memory of problems in S+3.x (x < 4) is still
affecting decisions today.
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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