[Rcpp-devel] Debugging Rcpp code

[Romain Francois]

That's the one;

You might like to di something like:

std::vector< std::vector<double> > groups( max(i) ) ;

you'll pay for the traversal of the max, but then you don't need to resize.




Calling fun() is going to be costly too (probably what will dominate). 
specially because of our internal::try_catch thing. See in 
Evaluator.cpp. that's a mess.

We should have something for faster evaluations, so that we would make 
the call and just use Rf_eval.



It will become more fun when we "apply" c++ functions. ^^

Romain


Le 16/11/12 16:03, Hadley Wickham a écrit :
> Ooops, I completely misinterpreted the std::vector API.  To insert the
> elements I need to do:
>
>    for(x_it = x.begin(), i_it = i.begin(); x_it != x.end(); ++x_it, ++i_it) {
>      int i = *i_it;
>      if (i > groups.size()) {
>        groups.resize(i);
>      }
>      groups[i - 1].push_back(*x_it);
>    }
>
> Hadley
>
> On Fri, Nov 16, 2012 at 8:36 AM, Hadley Wickham <h.wickham at gmail.com> wrote:
>> Hi all,
>>
>> I'm attempting to write a simple version of tapply in C++ (see
>> attached).  However, when I run tapply2(1, 1, sum) (which should
>> return 1), R segfaults.  If I run R with gdb, I get the following
>> stack trace:
>>
>> #0  0x03942120 in tapply2 (x=@0xbfffda68, i=@0xbfffda58,
>> fun=@0xbfffda50) at tapply.cpp:22
>> #1  0x0394298a in Rcpp::CppFunction_WithFormals3<Rcpp::Vector<14>,
>> Rcpp::Vector<14>, Rcpp::Vector<13>, Rcpp::Function>::operator()
>> (this=0x7f71c0, args=0xbfffdabc) at Module_generated_CppFunction.h:311
>> #2  0x0385b8b1 in InternalFunction_invoke ()
>> ...
>>
>> where line 22 is return out;
>>
>> I suspect it's something to do with the my coercion between
>> std::vector and NumericVector to call the function, or between the
>> SEXP output and NumericVector to store the output:
>>
>>    std::vector< std::vector<double> >::iterator g_it = groups.begin();
>>    NumericVector::iterator o_it = out.begin();
>>    for(; g_it != groups.end(); ++g_it, ++o_it) {
>>      *o_it = as<double>(fun(wrap(*g_it)));
>>    }
>>
>> I'd appreciate any hints as to how to solve this particular problem,
>> as well as any general debugging strategies.
>>
>> Thanks!
>>
>> Hadley
>>
>> --
>> RStudio / Rice University
>> http://had.co.nz/
>
>
>


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