[Rd] can't get names of R_env

[Prof Brian Ripley]

You are still misrepresenting the manual, which is discourteous to the 
altruistic people who wrote it.

You have still not explained why you 'need' help with internal parts 
of R that only R-core can exploit.  .Internal is a private interface: 
.External is the documented public version.

In the light of those, I suspect you will find the 'someone' who 'can 
clarify' unwilling to give free consultancy to someone who does not 
use a real name (real names are capitalized) nor a signature block.

On Fri, 9 Jan 2009, torpedo fisken wrote:

> Thanks for your reply.
>
> 2009/1/5 Prof Brian Ripley <ripley at stats.ox.ac.uk>:
>> 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'.
>
> Yes, I can see their implementation in src/main/envir.c.
> But I'm still somewhat lost concerning the innerworkings of the .R <->
> .c interface.
> Especially the passing of the R_env parameter from R.
>
> I'll try to explain what puzzles me as concisely as possible
> -----------------------------------------------------
> i.e
> the optim() prototype is
> optim <- function(par, fn, gr = NULL, ...,
>                  method = c("Nelder-Mead", "BFGS", "CG", "L-BFGS-B", "SANN"),
>                  lower = -Inf, upper = Inf,
>                  control = list(), hessian = FALSE)
>
> This makes an .Internal method call with
> .Internal(optim(par, fn1, gr1, method, con, lower, upper))
> This has seven args.

Not so: it has one arguent, a call.

> An by "src/names.c" this will use the do_optim() from src/main/optim.c
> which has the following protype
> SEXP attribute_hidden do_optim(SEXP call, SEXP op, SEXP args, SEXP rho);
> This has 4 args.
>
> According to the R-ints all .Internal that calls c-code will call
> dispatchOrEval() in src/eval.c
> http://cran.r-project.org/doc/manuals/R-ints.html#Argument-evaluation

According to you, but not according to the manual.

> But the arguments (there are 8), remains quite obscure for me.
> And I'm having some problems tracking down the .Internal function
> definition in the sourcetree.
>
> Can someone clarify what happens in between .
> .Internal(optim(...))  to do_optim(...)
>
> Thanks again.
>
>> 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.

-- 
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