Hello,
I'm starting to write a C function that gets
a list and a matrix from R. I'm using .Call
because I've undertood that this is recommended
to handle lists (am I wrong?). My problem is that I
can pass the matrix as a vector, but not as a 2D array.
For example, in the following simple C program:
#include <R.h>
#include <Rdefines.h>
SEXP printListElement(SEXP list, SEXP stat)
{
SEXP elmt = R_NilValue, names = getAttrib(list, R_NamesSymbol);
int i; double g1, g2, g3, s1, s2, s3;
for (i = 0; i < length(list); i++) {
elmt = VECTOR_ELT(list, i);
g1 = REAL(VECTOR_ELT(list, i))[0];
s1 = REAL(stat)[12];
printf("%ld %f %f \n", i, g1, s1);
}
return elmt;
}
I can get the 13th element of stat, but what should
I do to write something like:
s1 = REAL(stat)[1][5]
?
I've tried SEXP *stat, SEXP stat[] etc.
I can always calculate the one-dimensional index
from the line and column indices, but referencing
with 2 indices would be more simple.
(The C program is called from the R function:> testR
function (lista,stat)
{
a <- .Call("printListElement",lista,stat)
}
Thanks
Dr. Agustin Lobo
Instituto de Ciencias de la Tierra (CSIC)
Lluis Sole Sabaris s/n
08028 Barcelona SPAIN
tel 34 93409 5410
fax 34 93411 0012
alobo at ija.csic.es
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>>>>> "AgusL" == Agustin Lobo <alobo at ija.csic.es> writes:AgusL> Hello, AgusL> I'm starting to write a C function that gets AgusL> a list and a matrix from R. I'm using .Call AgusL> because I've undertood that this is recommended AgusL> to handle lists (am I wrong?). My problem is that I AgusL> can pass the matrix as a vector, but not as a 2D array. Yes, they are vectors in one sense, the main reason being that C does not have really have 2D arrays [another reason being that Fortran has this equivalence by definition]. The example you give is just a typical implementation of matrices in C, but AFAIK not at all the most common one for numerical computation. The R functions row() and col() call the following C function (from src/main/array.c) which should you how to deal with arrays: --------------------------------------------------------------- SEXP do_rowscols(SEXP call, SEXP op, SEXP args, SEXP rho) { SEXP ans; int i, j, nr, nc; if (length(args) != 1) error("incorrect number of args to row/col"); if (!isMatrix(CAR(args))) error("a matrix is required as arg to row/col"); nr = nrows(CAR(args)); nc = ncols(CAR(args)); ans = allocMatrix(INTSXP, nr, nc); switch (PRIMVAL(op)) { case 1: for (i = 0; i < nr; i++) for (j = 0; j < nc; j++) INTEGER(ans)[i + j * nr] = i + 1; break; case 2: for (i = 0; i < nr; i++) for (j = 0; j < nc; j++) INTEGER(ans)[i + j * nr] = j + 1; break; } return ans; } --------------------------------------------------------------- For that case (and in others), people may like to use C macros, e.g., #define ANS(I_,J_) INTEGER(ans)[I_ + J_ * nr] would allow you to have ANS(i,j) = i + 1; ... ANS(i,j) = j + 1; in the above function. But note that this macros relies on `nr' being defined and having the correct value. One reason we tend not to use them. Martin Maechler <maechler at stat.math.ethz.ch> http://stat.ethz.ch/~maechler/ Seminar fuer Statistik, ETH-Zentrum LEO D10 Leonhardstr. 27 ETH (Federal Inst. Technology) 8092 Zurich SWITZERLAND phone: x-41-1-632-3408 fax: ...-1228 <>< -.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.- r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html Send "info", "help", or "[un]subscribe" (in the "body", not the subject !) To: r-help-request at stat.math.ethz.ch _._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._