[This is the third post in a three part series that demonstrates how to create an R package that includes RcppArmadillo source code. Follow these links for part one and part two]
So we now have an R package that is compiled and delivers a linked C++ function into your R session (when loaded with the usual library( ... ) command).
One thing that’s going to happen when you use getCoef in the real world is that you’re going to have problems with missing values.
If your missing value is in X, you will see:
R> getCoef(c(NA, X[-1]), Y) Error in getCoef(c(NA, X[-1]), Y) : BLAS/LAPACK routine 'DLASCL' gave error code -4
If the missing value is in Y, you will see (the harder to diagnose):
R> getCoef(X, c(NA, Y[-1]))
[,1]
[1,] NA
[2,] NA
There are two possible solutions: changing the code to check to see if the variables that have been passed include any NA values; or adding a function that fills in NA values somehow. The point of this blog is to show what happens when we add a new function — and how to do it right — so we’re going to take the second path.
A short google reveals that this is a solved problem: Romain Francois provided this solution on stackoverflow:
//[[Rcpp::export]]
NumericVector naLocf(NumericVector x) {
double *p=x.begin(), *end = x.end() ;
double v = *p ; p++ ;
while( p < end ){
while( p<end && !NumericVector::is_na(*p) ) p++ ;
v = *(p-1) ;
while( p<end && NumericVector::is_na(*p) ) {
*p = v ;
p++ ;
}
}
return x;
}
If you're like me, you'll be thinking: 'great, problem solved'.
Not quite … but let's try it to see how it breaks.
Save the above snippet into file naLOCF.cpp, inside the /PAX/src/ folder, and recompile the package with:
$ CMD build C:\Users\abc\Dropbox\R\packages\PAX
You should see something like:
$ naLOCF.cpp:1:15: fatal error: Rcpp: No such file or directory
Followed by a warning that compilation has been terminated. Mine says the following:
compilation terminated.
make: *** [C:/PROGRA~1/R/R-35~1.1/etc/x64/Makeconf:215: naLOCF.o] Error 1
ERROR: compilation failed for package 'PAX'
* removing 'C:/Users/abc/AppData/Local/Temp/RtmpA7sPSX/Rinst36441e58481d/PAX'
In R CMD INSTALL
-----------------------------------
ERROR: package installation failed
So what went wrong?
We forgot the compileAttributes() and package_native_routine_registration_skeleton steps.
Recall from part two that you need to open an R terminal and do the following:
R> library(RcppArmadillo)
R> setwd("C:\Users\abc\Dropbox\R\packages\PAX")
R> Rcpp::compileAttributes()
R> tools::package_native_routine_registration_skeleton(dir = "path-to-PAX", character_only = FALSE)
NOTE this time you must set character_only = FALSE
Now copy the output to the init.c file, and try again:
$ CMD build C:\Users\abc\Dropbox\R\packages\PAX
