Rcpp crashes RStudio

Question

I have a simple rcpp file that crashes (or so it seems) RStudio.

C++ Code

Here is the .cpp file (saved as Test/CppHelpers.cpp):

#include <Rcpp.h>

// [[Rcpp::plugins("cpp11")]]

using namespace Rcpp;

// [[Rcpp::export]]
NumericMatrix generateCombinations(const NumericMatrix& odds) {
  int n = odds.rows();
  int N = n*n*n;

  IntegerVector v1(n);
  std::iota(v1.begin(), v1.end(), 0);
  IntegerVector v2(n*n);
  v2 = rep_each(v1,n);

  NumericVector col0(N);
  NumericVector col1(N);
  NumericVector col2(N);
  for(int k = 0; k <= N; ++k) {
    int ind0 = k / (n*n);
    int ind1 = k % (n*n);
    ind1 = v2[ind1];
    int ind2 = k % n;

    col0[k] = odds(ind0,0);
    col1[k] = odds(ind1,1);
    col2[k] = odds(ind2,2);
  }

  NumericMatrix out(N,3);
  out(_,0) = col0;
  out(_,1) = col1;
  out(_,2) = col2;

  return out;
}

R Code

Here is my .R file where I merely source the above file and perform a basic test

Rcpp::sourceCpp("Test/CppHelpers.cpp")
n <- 9
odds <- matrix(1:n,ncol=3)
my_combs <- generateCombinations(odds)

And this actually works as expected. However, every time I run the code, after a short while, it consistently crashes RStudio.

I do not really understand why those crashes arise and how to remedy it (especially since it does not crash right away). Any guidance would be appreciated.

---

Session Info

> sessionInfo()
R version 3.5.1 (2018-07-02)
Platform: x86_64-w64-mingw32/x64 (64-bit)
Running under: Windows >= 8 x64 (build 9200)

Matrix products: default

locale:
[1] LC_COLLATE=German_Germany.1252  LC_CTYPE=German_Germany.1252    LC_MONETARY=German_Germany.1252
[4] LC_NUMERIC=C                    LC_TIME=German_Germany.1252    

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     

loaded via a namespace (and not attached):
[1] compiler_3.5.1 tools_3.5.1    yaml_2.2.0  

Answer 1

You have a very basic indexing error: k cannot reach N so make it k < N.

Here is the output once you correct that:

R> Rcpp::sourceCpp("/tmp/so53936159.cpp")

R> n <- 9

R> odds <- matrix(1:n,ncol=3)

R> my_combs <- generateCombinations(odds)
R> my_combs
      [,1] [,2] [,3]
 [1,]    1    4    7
 [2,]    1    4    8
 [3,]    1    4    9
 [4,]    1    5    7
 [5,]    1    5    8
 [6,]    1    5    9
 [7,]    1    6    7
 [8,]    1    6    8
 [9,]    1    6    9
[10,]    2    4    7
[11,]    2    4    8
[12,]    2    4    9
[13,]    2    5    7
[14,]    2    5    8
[15,]    2    5    9
[16,]    2    6    7
[17,]    2    6    8
[18,]    2    6    9
[19,]    3    4    7
[20,]    3    4    8
[21,]    3    4    9
[22,]    3    5    7
[23,]    3    5    8
[24,]    3    5    9
[25,]    3    6    7
[26,]    3    6    8
[27,]    3    6    9
R> 

Repaired code with the included R example below.

#include <Rcpp.h>

// [[Rcpp::plugins("cpp11")]]

using namespace Rcpp;

// [[Rcpp::export]]
NumericMatrix generateCombinations(const NumericMatrix& odds) {
  int n = odds.rows();
  int N = n*n*n;

  IntegerVector v1(n);
  std::iota(v1.begin(), v1.end(), 0);
  IntegerVector v2(n*n);
  v2 = rep_each(v1,n);

  NumericVector col0(N);
  NumericVector col1(N);
  NumericVector col2(N);
  for(int k = 0; k < N; ++k) {
    int ind0 = k / (n*n);
    int ind1 = k % (n*n);
    ind1 = v2[ind1];
    int ind2 = k % n;

    col0[k] = odds(ind0,0);
    col1[k] = odds(ind1,1);
    col2[k] = odds(ind2,2);
  }

  NumericMatrix out(N,3);
  out(_,0) = col0;
  out(_,1) = col1;
  out(_,2) = col2;

  return out;
}

/*** R
n <- 9
odds <- matrix(1:n,ncol=3)
my_combs <- generateCombinations(odds)
*/