R/Python + C++

In some recent projects, I was working on using algorithms implemented in C++ from R and Python. Basically the idea is: Python and R are great languages for scripting but they are slow as molasses. So, it may make sense to develop the time consuming algorithms in C++ while driving the algorithm from R or Python.

R and C++: Rcpp.

The standard way to build interfaces between R and C++ code is to use Rcpp [1,2].

It is possible to directly interface R with low-level C code, This will require a lot of code and knowledge of R internals. Rcpp automates a lot of this. E.g. Rcpp will take care of translating an R vector into a C++ vector.

Rcpp supports both small fragments of C++ code passed on as an R string to more coarse-grained file based approach [3]. For Windows, you need to download the GNU compilers [4].

If you are new to both  Rcpp and to building your own R packages [5] things may be a bit overwhelming.

Rstudio can help a lot. It supports a lot of very useful tasks:

• Syntax coloring for C++ code. 
• Building projects.
• Git version control.
• Documentation tools (rmarkdown and bookdown). My documentation is also a good test: it executes almost all of the code when building the document.

Editing C++ code in RStudio

Basically I never have to leave RStudio.

I have added an alternative driver file for my C++ code so I can debug it in Visual Studio. I used it only a few times: most of the time I just used RStudio.

Python and C++: pybind11

pybind11 [6] is in many respects similar to Rcpp, although it requires a little bit more programming to bridge the gap between Python and C++.

In the beginning of the above Youtube video [7], the presenter compares pybind11 with some of the alternatives:

• SWIG: author of SWIG says: don't use it
• ctypes: call c functions but not c++
• CFFI: call c functions
• Boost.Python: support for older C++ standards, but not much maintained
• pybind11: modern 

As with Rcpp, calling the compiler is done through running a build or setup script. For Rcpp I used the GNU compilers, while pybind11/pip install supports the Visual Studio C++ compiler. This also means that if you have little experience with both pybind11 and creating packages, the learning curve may be steep.

References

1. http://www.rcpp.org
2. Dirk Eddelbuettel, Seamless R and C++ Integration with Rcpp, Springer, 2013
3. Chapter: Rewriting R code in C++, https://adv-r.hadley.nz/rcpp.html 
4. Hadley Wickham, R packages, O'Reilly, 2015 
5. https://cran.r-project.org/bin/windows/Rtools/
6. https://pybind11.readthedocs.io/en/master/
7. Robert Smallshire, Integrate Python and C++ with pybind11, https://www.youtube.com/watch?v=YReJ3pSnNDo