The R Project SVN R

\name{example}

\alias{example}

\title{Run an Examples Section from the Online Help}

\description{

  Run all the \R code from the \bold{Examples} part of \R's online help

  topic \code{topic} with two possible exceptions, \code{dontrun} and

  \code{dontshow}, see Details below.

}

\usage{

example(topic, package = .packages(), lib.loc = NULL,

        local = FALSE, echo = TRUE, verbose = getOption("verbose"),

        setRNG = FALSE,

        prompt.echo = paste(abbreviate(topic, 6),"> ", sep=""))

}

\arguments{

  \item{topic}{name or literal character string: the online

    \code{\link{help}} topic the examples of which should be run.}

  \item{package}{a character vector with package names.  By default,

    all packages in the search path are used.}

  \item{lib.loc}{a character vector of directory names of \R libraries,

    or \code{NULL}.  The default value of \code{NULL} corresponds to all

    libraries currently known.  If the default is used, the loaded

    packages are searched before the libraries.}

  \item{local}{logical: if \code{TRUE} evaluate locally, if \code{FALSE}

    evaluate in the workspace.}

  \item{echo}{logical;  if \code{TRUE}, show the \R input when sourcing.}

  \item{verbose}{logical;  if \code{TRUE}, show even more when running

    example code.}

  \item{setRNG}{logical or expression;  if not \code{FALSE}, the random

    number generator state is saved, then initialized to a specified state,

    the example is run and the (saved) state is restored.  \code{setRNG

      = TRUE} sets the same state as \code{R CMD \link{check}} does for

    running a package's examples.  This is currently equivalent to

    \code{setRNG = \{RNGkind("default", "default"); set.seed(1)\}}.}

  \item{prompt.echo}{character; gives the prompt to be used if

    \code{echo = TRUE}.}

}

\value{(the value of the last evaluated expression).}

\details{

  If \code{lib.loc} is not specified, the packages are searched for

  amongst those already loaded, then in the specified libraries.

  If \code{lib.loc} is specified, they are searched for only

  in the specified libraries, even if they are already loaded from

  another library.

  An attempt is made to load the package before running the examples,

  but this will not replace a package loaded from another location.

  If \code{local=TRUE} objects are not created in the workspace and so

  not available for examination after \code{example} completes: on the

  other hand they cannot clobber objects of the same name in the

  workspace.

  As detailed in the manual \emph{Writing \R Extensions}, the author of

  the help page can markup parts of the examples for two exception rules

  \describe{

    \item{\code{dontrun}}{encloses code that should not be run.}

    \item{\code{dontshow}}{encloses code that is invisible on help

      pages, but will be run both by the package checking tools,

      and the \code{example()} function.  This was previously

      \code{testonly}, and that form is still accepted.}

    }

}

\note{

  The examples can be many small files.  On some file systems it is

  desirable to save space, and the files in the \file{R-ex} directory

  of an installed package can be zipped up as a zip archive

  \file{Rex.zip}.

}

\author{Martin Maechler and others}

\seealso{\code{\link{demo}}}

\examples{

example(InsectSprays)

## force use of the standard package 'stats':

example("smooth", package="stats", lib.loc=.Library)

## set RNG *before* example as when R CMD check is run:

r1 <- example(quantile, setRNG = TRUE)

x1 <- rnorm(1)

u <- runif(1)

## identical randum numbers

r2 <- example(quantile, setRNG = TRUE)

x2 <- rnorm(1)

stopifnot(identical(r1, r2))

## but x1 and x2 differ since the RNG state from before example()

## differs and is restored!

x1; x2

}

\keyword{documentation}

\keyword{utilities}