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 search for the string “.Internal” within it.
callsInternalCode <- function(fn)
if(!require(stringr)) stop("stringr package required")
You can retrieve all the functions 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.
 "abbreviate" "agrep"
 "all.names" "all.vars"
 "anyDuplicated.default" "aperm"
EDIT: Tweaked the regex (the ‘.’ should have been escaped.)