You will have to read more carefully: an ENVSXP is nothing like a VECSXP,
and does not have the names of its entries in a names attribute.
You access variables in an environment via findVar() and friends,
including findVarInFrame: see 'Writing R Extensions'.
On Mon, 5 Jan 2009, torpedo fisken wrote:
Hi,
I'm quite knew in R, so I might not have the R specific jargon.
But here is my problem,
I'm trying to access and use variabels given by a function environment,
more specifically the rho in do_optim in src/main/optim.c
Very likely this is not the way to do whatever it is that you really want
to do.
According to the documentation
http://cran.r-project.org/doc/manuals/R-ints.html#The-_0027data_0027
the envsxp is defined as a tagged pairlist.
"ENVSXP: Pointers to the frame, enclosing environment and hash table
(NULL or a VECSXP). A frame is a tagged pairlist with tag the symbol
and CAR the bound value."
But I'm having troubles accessing the data.
I've written a small function called printNames that looks like
-----------------------
void printNames(SEXP list){
SEXP names = getAttrib(list, R_NamesSymbol);
int i;
Rprintf("List is of length:%d\n",length(list));
for (i = 0; i < length(list); i++)
Rprintf("name of id:%d\t%s\n",i,CHAR(STRING_ELT(names, i)));
}
-----------------------
This is basicly just a copy of
-----------------------
static SEXP getListElement(SEXP list, char *str)
{
SEXP elmt = R_NilValue, names = getAttrib(list, R_NamesSymbol);
int i;
for (i = 0; i < length(list); i++)
if (strcmp(CHAR(STRING_ELT(names, i)), str) == 0) {
elmt = VECTOR_ELT(list, i);
break;
}
return elmt;
}
-----------------------
But this crashes and looks like
-----------------------
List is of length:16
name of id:0 Xd???
name of id:1 Xd???
name of id:2
*** caught segfault ***
address 0x28, cause 'memory not mapped'
------------------------
I've just added printNames(rho) in the very first line of do_optim().
Futhermore I've checked that the typeof(rho) corresponds to the
#define ENVSXP 4 in Rinternals.h at line 84
Can anyone clarify how to access these enviroment variables.
I believe my problem lies in the sentence "A frame is a tagged
pairlist with tag the symbol and CAR the bound value."
Or more precisely, I don't quite understand the struct for env exp
--------------------------
struct envsxp_struct {
struct SEXPREC *frame;
struct SEXPREC *enclos;
struct SEXPREC *hashtab;
};
--------------------------
thanks in advance.
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--
Brian D. Ripley, rip...@stats.ox.ac.uk
Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/
University of Oxford, Tel: +44 1865 272861 (self)
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