Dirk Eddelbuettel — written Jan 5, 2013 — source
At its very essence, Rcpp permits easy access to native R objects at the C++ level. R objects can be - simple vectors, list or matrices; - compound data structures created from these; - objects of S3, S4 or Reference Class vintage; or - language objects as for example environments.
Accessing a function object is no different. And calling a function can be very useful. Maybe to pick up parameter initializations, maybe to access a custom data summary that would be tedious to recode, or maybe even calling a plotting routine. We already have examples for just about all of these use case in the Rcpp examples or unit tests shipping with the package.
So here were a just providing a simple example of calling a summary
function, namely the Tukey
But before we proceed, a warning. Calling a function is simple and tempting. It is also slow as there are overheads involved. And calling it repeatedly from inside your C++ code, possibly buried within several loops, is outright silly. This has to be slower than equivalent C++ code, and even slower than just the R code (because of the marshalling of data). Do it when it makes sense, and not simply because it is available.
 -4.043276 -0.682384 -0.002066 0.673325 4.328091
Now via this C++ code:
And unsurprisingly, calling the same function on the same data gets the same result:
 -4.043276 -0.682384 -0.002066 0.673325 4.328091Tweet