Rcpp compiler flags error with return value - clueless

Question

Im trying to speed up some R code with Rcpp functions. One function is giving me fits to compile and I am clueless to figure out why the compiler complains about the return argument. I declared the function to return NumericVector, the result is NumericVector and yet the compiler complains the return argument is invalid.

Rcpp is version 0.12.18, R is Microsoft Open R 3.5.3

cppFunction('NumericVector NNE(IntegerVector X, IntegerVector Y, IntegerVector XY, IntegerVector xy, NumericVector P, int radius ) {

  int n = X.size();
  NumericVector vN[n];
  NumericVector vSum[n];
  NumericVector vAvg[n];


  // for each xy determine neighborhood Sum and count (N)
  for(int i=0; i<n; i++) {
    vN[i] = 0.0;
    vSum[i] = 0.0;

    // traverse neighborhood, if the xy exists in the input
    // vector then accumulate the values, otherwise ignore

    for(int dx=-1*radius; dx<=radius; dx++) {
      for(int dy=-1*radius; dy<=radius; dy++) {

        // construct an xy index for the neighborhood die
        xy[0] = ( (X[i]+dx) * 10000 ) + (Y[i]+dy);

        // check to see if index above exists in input set
        IntegerVector m = Rcpp::match(xy, XY);

        // if valid then accumulate and count
        if(m[0] != NA_INTEGER) {
          vN[i] = vN[i] + 1.0;
          vSum[i] = vSum[i] + P[ m[0] ];
        }
      }
    }

    vAvg[i] = vSum[i] / vN[i];
  }

  return vAvg;
}')

The confusing compiler message is as follows:

C:/RBuildTools/3.5/mingw_64/bin/g++ -m64 -I"C:/PROGRA~1/MICROS~3/ROPEN~1/R-35~1.3/include" -DNDEBUG   -I"D:/Users/ka/Documents/R/win-library/3.5/Rcpp/include" -I"D:/Users/ka/AppData/Local/Temp/4/RtmpeGKfUg/sourceCpp-x86_64-w64-mingw32-0.12.18"   -I"C:/a/w/1/s/vendor/extsoft/include"     -O2 -Wall  -mtune=core2 -c filefcc651c7fa9.cpp -o filefcc651c7fa9.o
filefcc651c7fa9.cpp: In function 'Rcpp::NumericVector NNE(Rcpp::IntegerVector, Rcpp::IntegerVector, Rcpp::IntegerVector, Rcpp::IntegerVector, Rcpp::NumericVector, int)':
filefcc651c7fa9.cpp:42:10: error: invalid conversion from 'Rcpp::NumericVector* {aka Rcpp::Vector<14, Rcpp::PreserveStorage>*}' to 'const int&' [-fpermissive]
   return vAvg;
          ^
In file included from D:/Users/ka/Documents/R/win-library/3.5/Rcpp/include/Rcpp/Vector.h:52:0,
                 from D:/Users/ka/Documents/R/win-library/3.5/Rcpp/include/Rcpp.h:40,
                 from filefcc651c7fa9.cpp:1:
D:/Users/ka/Documents/R/win-library/3.5/Rcpp/include/Rcpp/vector/Vector.h:128:5: note: initializing argument 1 of 'Rcpp::Vector<RTYPE, StoragePolicy>::Vector(const int&) [with int RTYPE = 14; StoragePolicy = Rcpp::PreserveStorage]'
     Vector( const int& size ) {
     ^
make: *** [C:/PROGRA~1/MICROS~3/ROPEN~1/R-35~1.3/etc/x64/Makeconf:215: filefcc651c7fa9.o] Error 1
Error in sourceCpp(code = code, env = env, rebuild = rebuild, cacheDir = cacheDir,  : 
  Error 1 occurred building shared library.

Answer 1

You had a miniscule error rendering the variable "bad" as far as the compiler is concerned, and you then misunderstood the rejected return of the "bad" variable as a different issue.

It happens. We have all been there.

Here is the repaired code. In short, you needed NumeriVector x(n); with round instead of squared parens (as the latter denote arrays in C and then C++).

Code

I also turned it into input for sourceCpp() which is easier given the length of the functions.

#include <Rcpp.h>

using namespace Rcpp;

// [[Rcpp::export]]
NumericVector NNE(IntegerVector X, IntegerVector Y, IntegerVector XY,
                  IntegerVector xy, NumericVector P, int radius ) {

  int n = X.size();
  NumericVector vN(n);
  NumericVector vSum(n);
  NumericVector vAvg(n);

  // for each xy determine neighborhood Sum and count (N)
  for(int i=0; i<n; i++) {
    vN[i] = 0.0;
    vSum[i] = 0.0;

    // traverse neighborhood, if the xy exists in the input
    // vector then accumulate the values, otherwise ignore

    for(int dx=-1*radius; dx<=radius; dx++) {
      for(int dy=-1*radius; dy<=radius; dy++) {

        // construct an xy index for the neighborhood die
        xy[0] = ( (X[i]+dx) * 10000 ) + (Y[i]+dy);

        // check to see if index above exists in input set
        IntegerVector m = Rcpp::match(xy, XY);

        // if valid then accumulate and count
        if(m[0] != NA_INTEGER) {
          vN[i] = vN[i] + 1.0;
          vSum[i] = vSum[i] + P[ m[0] ];
        }
      }
    }

    vAvg[i] = vSum[i] / vN[i];
  }

  return vAvg;
}

/*** R
cat("Built\n")
*/

Output

As we have no reference data, I can only show that it built:

R> sourceCpp("~/git/stackoverflow/61377960/answer.cpp")

R> cat("Built\n")
Built
R>