How to access the help/documentation .rd source files in R?

Question

In R, one very neat feature is that the source code of functions is accessible as objects in the workspace.

Thus, if I wanted to know the source code of, for example, grep() I can simply type grep into the console and read the code.

Similarly, I can read the documentation for grep by typing ?grep into the console.

Question: How can I get the source code for the documentation of a function? In other words, where do I find the .rd files?

I find studying the source of well-written code an excellent way of learning the idioms. Now I want to study how to write documentation for some very specific cases. I have not been able to find the documentation files for any of the base R functions in my R installation. Perhaps I have been looking in the wrong place.

Answer 1

It seems you can extract the Rd sources from an installed R. I'm using R-devel (2011-09-05 r56942).

Get the database of Rd for the base package.

library(tools)
db <- Rd_db("base")

Search for "grep.Rd" in the names of the Rd DB, for example:

grep("grep.Rd", names(db), value = TRUE)
[1] "d:/murdoch/recent/R64/src/library/base/man/agrep.Rd"
[2] "d:/murdoch/recent/R64/src/library/base/man/grep.Rd" 

Get just the Rd object for grep.

db[grep("/grep.Rd", names(db))]
$`d:/murdoch/recent/R64/src/library/base/man/grep.Rd`
\title{Pattern Matching and Replacement}
\name{grep}
\alias{grep}
\alias{grepl}
\alias{sub}
\alias{gsub}
\alias{regexpr}
\alias{gregexpr}
\alias{regexec}
\keyword{character}
\keyword{utilities}
\description{
\code{grep}, \code{grepl}, \code{regexpr} and \code{gregexpr} search
for matches to argument \code{pattern} within each element of a
character vector: they differ in the format of and amount of detail in
the results.

\code{sub} and \code{gsub} perform replacement of the first and all
matches respectively.
}\usage{
...
...

There are tools for getting the components from the Rd objects, so you can refine searching to keywords or name, see examples in ?Rd_db and try this.

lapply(db, tools:::.Rd_get_metadata, "name")