The R Project SVN R

% File src/library/utils/man/example.Rd

% Part of the R package, https://www.R-project.org

% Copyright 1995-2019 R Core Team

% Distributed under GPL 2 or later

\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 possible exceptions \code{dontrun},

  \code{dontshow}, and \code{donttest}, see \sQuote{Details} below.

}

\usage{

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

        character.only = FALSE, give.lines = FALSE, local = FALSE,

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

        setRNG = FALSE, ask = getOption("example.ask"),

        prompt.prefix = abbreviate(topic, 6),

        run.dontrun = FALSE, run.donttest = interactive())

}

\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 giving the package names to look

    into for the topic, or \code{NULL} (the default), when all packages on

    the \link{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{character.only}{a logical indicating whether \code{topic} can be

    assumed to be a character string.}

  \item{give.lines}{logical: if true, the \emph{lines} of the example

    source code are returned as a character vector.}

  \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

    \command{R CMD \link{check}} does for

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

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

  \item{ask}{logical (or \code{"default"}) indicating if

    \code{\link{devAskNewPage}(ask = TRUE)} should be called

    before graphical output happens from the example code.  The value

    \code{"default"} (the factory-fresh default) means to ask if

    \code{echo == TRUE} and the graphics device appears to be

    interactive.  This parameter applies both to any currently opened

    device and to any devices opened by the example code.}

  \item{prompt.prefix}{character; prefixes the prompt to be used if

    \code{echo = TRUE}.}

  \item{run.dontrun}{logical indicating that \verb{\dontrun}

    should be ignored.}

  \item{run.donttest}{logical indicating that \verb{\donttest}

    should be ignored.}

}

\value{

  The value of the last evaluated expression, unless \code{give.lines}

  is true, where a \code{\link{character}} vector is returned.

}

\details{

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

  amongst those already loaded, then in the libraries given by

  \code{\link{.libPaths}()}.  If \code{lib.loc} is specified, packages

  are searched for only in the specified libraries, even if they are

  already loaded from another library.  The search stops at the first

  package found that has help on the topic.

  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 overwrite 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 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.}

    \item{\code{donttest}}{encloses code that typically should be run,

      but not during package checking.  The default

      \code{run.donttest = \link{interactive}()}

      leads \code{example()} use in other help

      page examples to skip \verb{\donttest} sections appropriately.}

  }

}

\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 random 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

## Exploring examples code:

## How large are the examples of "lm...()" functions?

lmex <- sapply(apropos("^lm", mode = "function"),

               example, character.only = TRUE, give.lines = TRUE)

sapply(lmex, length)

}

\keyword{documentation}

\keyword{utilities}