[Rcpp-devel] Evaluating a call in a particular environment

[Dirk Eddelbuettel]

On 20 May 2010 at 16:54, Douglas Bates wrote:
| A short version of this question is "can I evaluate an Rcpp::Language
| instance in an Rcpp::Environment instance"?  Initially I thought this
| was a given but on looking closer at the unit tests I don't see how
| exactly it would be done.
| 
| A second short version of this question is "could someone, probably
| Romain, remind me what is done to activate the debugging code in Rcpp
| or point me to the documentation for it?".

Two simple macros are in RcppCommon.h:

// simple logging help
#define RCPP_DEBUG_LEVEL 0

#ifndef logTxt
	#if RCPP_DEBUG_LEVEL > 0
		#define logTxt(x) ::logTxtFunction(__FILE__, __LINE__, x);
	#else
		#define logTxt(x)
	#endif
#endif

#if RCPP_DEBUG_LEVEL > 0
	#define RCPP_DEBUG( fmt , ... ) Rprintf( "%s:%d " fmt "\n" , __FILE__, __LINE__,##__VA_ARGS__ ) ;
#else
	#define RCPP_DEBUG( fmt , ... )
#endif

So by flipping RCPP_DEBUG_LEVEL from 0 to 1 or greater you get
these. logTxtFunction is in RcppCommon.cpp:

void logTxtFunction(const char* file, const int line, const char* expression) {
    Rprintf("%s:%d %s\n", file, line, expression);
}

That was the easy part. I think I pass on the long version... That looks a
little hairy and I am only one coffee into the day...

Dirk


| The long version follows:
| 
| In the lme4a package (only on R-forge and requiring the R-forge
| version of the Matrix package) the nlmer function to fit nonlinear
| mixed-effects models has a nonlinear model, expressed as a call, and
| an environment in which to evaluate this call.  The operation of
| evaluating the deviance of the model involves changing the contents of
| some numeric vectors in this environment then evaluating the call.
| 
| The nlmerResp class is declared (in lme4a/src/mer.h) as
|     class nlmerResp : public rwResp {
| 	Rcpp::Environment nlenv;
| 	Rcpp::Language nlmod;
| 	Rcpp::CharacterVector pnames;
|     public:
| 	nlmerResp(Rcpp::S4 xp);
| 	void updateMu(Rcpp::NumericVector const &gamma);
|     };
| 
| and initialized from an Rcpp::S4 object.  I have some debugging code
| in the current version of the updateMu method to check that the values
| in the environment are what I expect them to be
| > nm1 <- lme4a:::nlmer2(circumference ~ SSlogis(age, Asym, xmid, scal) ~ 0 + Asym + xmid + scal + (0 + Asym|Tree), Orange, start = c(Asym = 200, xmid = 725, scal = 350))
| > .Call("nlmerDeEval", nm1)
| past initialization of nlmerDe object
| gamma after offset: 0, 0, 0, 0, 0
| u: 0, 0, 0, 0, 0
| b: 0, 0, 0, 0, 0
| gamma after reUpdate: 0, 0, 0, 0, 0
| gamma after feUpdate: 200, 200, 200, 200, 200
| gamma in resp::updateMu: 200, 200, 200, 200, 200
| p = 0, parameter name = Asym
| current: 200, 200, 200, 200, 200
| updated: 200, 200, 200, 200, 200
| p = 1, parameter name = xmid
| current: 725, 725, 725, 725, 725
| updated: 725, 725, 725, 725, 725
| p = 2, parameter name = scal
| current: 350, 350, 350, 350, 350
| updated: 350, 350, 350, 350, 350
| 
| Before evaluation
| Error in cpp_exception(message = "object 'xmid' not found", class =
| "Rcpp::eval_error") :
|   object 'xmid' not found
| 
| So I am a bit surprised at xmid not being found because I just
| modified it.  The objects at the R level are
| 
| > nm1 at resp@nlmod
| SSlogis(age, Asym, xmid, scal)
| > class(nm1 at resp@nlmod)
| [1] "call"
| > ls.str(nm1 at resp@nlenv)
| age :  num [1:35] 118 484 664 1004 1231 ...
| Asym :  num [1:35] 200 200 200 200 200 200 200 200 200 200 ...
| scal :  num [1:35] 350 350 350 350 350 350 350 350 350 350 ...
| xmid :  num [1:35] 725 725 725 725 725 725 725 725 725 725 ...
| 
| and I can evaluate the call in R
| 
| > head(eval(nm1 at resp@nlmod, nm1 at resp@nlenv))
| [1]  30.00804  66.87019  91.30771 137.87260 161.86760 172.79186
| 
| I am trying to evaluate the call in the C++ code as
| 
|    NumericVector rr = nlmod.eval(nlenv);
| 
| which, I assume, expands to
| 
|   NumericVector rr = nlmod.eval(SEXP(nlenv));
| 
| Is there some trick I am missing?
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-- 
  Regards, Dirk