Which functions in R base call internal code?

In a recent question on Stack Overflow about speeding up group-by operations, Marek wondered which functions called .Internal code (and consequently were fast). I was surprised to see that there appears to be no built-in way to check whether or not this is the case (though is.primitive is available for primitive functions).

Writing such a function is quite straight forward. We simply examine the contents of the function body, and serach for the string “.Internal” within it.

callsInternalCode <- function(fn) { +++if(!require(stringr)) stop("stringr package required") +++any(str_detect(capture.output(body(fn)), ".Internal")) }

You can retrieve all the function in the base package with this one-liner taken from an example on the Filter help page.

funs <- Filter(is.function, sapply(ls(baseenv()), get, baseenv()))

Now getting the list of functions that call internal code is easy.

names(funs)[sapply(funs, callsInternalCode)] [1] "abbreviate" "agrep" [3] "all.names" "all.vars" [5] "anyDuplicated.default" "aperm" ...