On Sat, Apr 26, 2008 at 11:38 AM, Prof Brian Ripley <[EMAIL PROTECTED]> wrote: > On Sat, 26 Apr 2008, Ramon Diaz-Uriarte wrote: > > > > On Sat, Apr 26, 2008 at 3:19 AM, Duncan Murdoch <[EMAIL PROTECTED]> > wrote: > > > > > Ramon Diaz-Uriarte wrote: > > > > > > > > > > Dear All, > > > > > > > > In a package, I am using ".C" to call some C functions. In one case, > > > > the number of elements of the return vectors are not known in R before > > > > the C call. (Two of the vectors are integers, the third is vector of > > > > character strings). > > > > > > > > Passing from R a vector of the maximum possible size would be a huge > > > > waste. I understand one alternative is to use ".Call", but I'd rather > > > > avoid it if I can (all of the code seems working except for the return > > > > of values into R). Another would be to write to a file from C and then > > > > read that into R, but this looks very ugly. Are there any other > > > > reasonable alternatives, or should I just use .Call? > > > > > > > > > > > > > > > > > > .Call is usually easiest, but another possibility is to have two entry > > > points: one to calculate how much space you need, a second to pass in a > > > vector that's the right size to hold the result. > > > > > > > > > > > > You mean making two successive calls to the C code? The problem is > > that the size of the result is not known until the result is obtained > > (in my C code, the underlying structure is a linked list that gets > > stretched as needed as the computation proceeds). So I would not know > > "where to leave the result from C" in between the two calls to C. > > > > But that is possible (you malloc the memory for a local copy in the rist > call), and rpart does something like it. >
Aha, thanks, I didn't know it was doable (or easy). I'll look at the rpart code. One further question, though, what is "the rist call"? Thanks, R. > > -- > Brian D. Ripley, [EMAIL PROTECTED] > 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 > -- Ramon Diaz-Uriarte Statistical Computing Team Structural Biology and Biocomputing Programme Spanish National Cancer Centre (CNIO) http://ligarto.org/rdiaz ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
