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/
#include <Rcpp.h>
using namespace Rcpp;
// [[Rcpp::export]]
NumericVector tapply2(NumericVector x, IntegerVector i, Function fun) {
std::vector< std::vector<double> > groups;
NumericVector::iterator x_it;
IntegerVector::iterator i_it;
for(x_it = x.begin(), i_it = i.begin(); x_it != x.end(); ++x_it, ++i_it) {
groups[*i_it].push_back(*x_it);
}
NumericVector out(groups.size());
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)));
}
return out;
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