r - Rcpp function check if missing value

Question

I'm converting R based code into Rcpp based code. The head of my function is:

NumericMatrix createMatrixOfLinkRatiosC(NumericMatrix matr, double threshold4Clean) {
int i,j; 
NumericMatrix myMatr(matr.nrow(),matr.ncol());
myMatr=matr;
....;

}

I want to handle call to the function where threshold4Clean is missing but I'm not finding how to do... Any help will be greatly appreciated.

Answer 1

R has both NaN and NA (which is really a special kind of NaN) for representing missing values. This is important to know because there are many functions that check if a value is NaN-y (NA or NaN):

Some truth tables for functions from the R/C API (note the frustrating lack of consistency)

+---------------------+
| Function | NaN | NA |
+---------------------+
| ISNAN    |  t  | t  |
| R_IsNaN  |  t  | f  |
| ISNA     |  f  | t  |
| R_IsNA   |  f  | t  |
+---------------------+

and Rcpp:

+-------------------------+
| Function     | NaN | NA |
+-------------------------+
| Rcpp::is_na  |  t  | t  |
| Rcpp::is_nan |  t  | f  |
+-------------------------+

and from the R interpreter (note: Rcpp tries to match this, rather than the R/C API):

+---------------------+
| Function | NaN | NA |
+---------------------+
| is.na    |  t  | t  |
| is.nan   |  t  | f  |
+---------------------+

Unfortunately it's a confusing landscape, but this should empower you a bit.