How to call C function from R?

Question

How can you use some function written in C from R level using R data. eg. to use function like:

double* addOneToVector(int n, const double* vector) {
    dou         


        

Answer 1

First off, I wanted to thank both @m0nhawk and @Jan for their immensely useful contributions to this problem.

I tried both methods on my MacBook: first the one showed m0nhawk which requires creating a function in C (without the main method) and then compiling using R CMD SHLIB and then invoking the function from R using the .C command

Here's a small C code I wrote (not a pro in C - just learning in bits and pieces)

Step 1: Write the C Program

#include 
int func_test() {
    
    for(int i = 0; i < 5; i++) {
        printf("The value of i is: %d\n", i);
    }
    return 0;

}

Step 2: Compile the program using

R CMD SHLIB func_test.c

This will produce a func_test.so file

Step 3: Now write the R Code that invokes this C function from within R Studio

dyn.load("/users/my_home_dir/xxx/ccode/ac.so")
.C("func_test")

Step 4: Output:

.C("func_test") The value of i is: 0 The value of i is: 1 The value of i is: 2 The value of i is: 3 The value of i is: 4 list()

Then I tried the direct method suggested by Jan - using the RCpp package

library("Rcpp")
cppFunction("
NumericVector addOneToVector(NumericVector vector) {
  int n = vector.size();

  for (int i = 0; i < n; ++i)
    vector[i] = vector[i] + 1.0;

  return vector;
}")

# Test code to test the function
addOneToVector(c(1,2,3))

Both methods worked superbly. I can now start writing functions in C or C++ and use them in R

Thank you once again!