all' hileth', Hephaiste; didou d'areten te kai olbon.* --Homer, 7th century BCE

The premise of roxygen2 is simple: describe your functions in comments next to their definitions and roxygen2 will process your source code and comments to produce Rd files in the man/ directory. Here's a simple example from the stringr package:

#' The length of a string (in characters).
#'
#' @param string input character vector
#' @return numeric vector giving number of characters in each element of the
#'   character vector.  Missing strings have missing length.
#' @seealso \code{\link{nchar}} which this function wraps
#' @export
#' @examples
#' str_length(letters)
#' str_length(c("i", "like", "programming", NA))
str_length <- function(string) {
  string <- check_string(string)

  nc <- nchar(string, allowNA = TRUE)
  is.na(nc) <- is.na(string)
  nc
}

When you roxygenise() (or devtools::document()) your package these comments will be automatically transformed to the Rd file you need to pass R CMD check:

\name{str_length}
\alias{str_length}
\title{The length of a string (in characters).}
\usage{str_length(string)}
\arguments{
  \item{string}{input character vector}
}
\description{
The length of a string (in characters).
}
\seealso{\code{\link{nchar}} which this function wraps}
\value{
  numeric vector giving number of characters in each element of the
  character vector.  Missings string have missing length.
}
\examples{
str_length(letters)
str_length(c("i", "like", "programming", NA))
}

To get the current released version from CRAN:

install.packages("roxygen2")

To get the current development version from github:

# install.packages("devtools")
devtools::install_github("klutometis/roxygen")

Roxygen does a live analysis of your source code: it loads all the code in your package, so it can create documentation using values in an R environment, not just source code. However, simulating package loading is rather tricky to do in general, so there are two ways to do it with roxygen:

• roxygen2::roxygenise() just sources all files in the R/ directory

• devtools::document() sources all files in the R/ directory, compiles source code in the src/ directory, loads data in the data/ directory and generally does an accurate job of simulating package loading.

If you have a simple package, you can use roxygenise(), but for anything more complicated, I recommend that you use document().

roxygen2 comes with four roclets, tools for parsing your source code and producing files useful for documenting your package:

• collate_roclet: allows you to add @include directives to ensure that files are loaded in the order they are needed

• namespace_roclet: creates your NAMESPACE automatically. 95% of the time all you need to do is label functions, methods and classes that you want to export with the @export tag

• rd_roclet: produces Rd files by inspecting both function definitions and roxygen2 comments in the source code

• vignette_roclet: builds vignettes using tools::buildVignette().

By default, roxygenise will run the first three, but you can choose which ones to run using the roclet parameter, or field Roxygen in your DESCRIPTION:

Roxygen: list(roclets = c("rd", "collate"))

• Hail, Hephaistos! Grant skill and weal.