example {utils} | R Documentation

## Run an Examples Section from the Online Help

### Description

Run all the R code from the Examples part of R's online help topic `topic` with two possible exceptions, `dontrun` and `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

`topic` | name or literal character string: the online `help` topic the examples of which should be run.
`package` | a character vector with package names. By default, all packages in the search path are used.
`lib.loc` | a character vector of directory names of R libraries, or `NULL`. The default value of `NULL` corresponds to all libraries currently known. If the default is used, the loaded packages are searched before the libraries.
`local` | logical: if `TRUE` evaluate locally, if `FALSE` evaluate in the workspace.
`echo` | logical; if `TRUE`, show the R input when sourcing.
`verbose` | logical; if `TRUE`, show even more when running example code.
`setRNG` | logical or expression; if not `FALSE`, the random number generator state is saved, then initialized to a specified state, the example is run and the (saved) state is restored. `setRNG = TRUE` sets the same state as `R CMD check` does for running a package's examples. This is currently equivalent to `setRNG = {RNGkind("default", "default"); set.seed(1)}`.
`prompt.echo` | character; gives the prompt to be used if `echo = TRUE`.

### Details

If `lib.loc` is not specified, the packages are searched for amongst those already loaded, then in the specified libraries. If `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 `local=TRUE` objects are not created in the workspace and so not available for examination after `example` completes: on the other hand they cannot clobber objects of the same name in the workspace.

As detailed in the manual Writing R Extensions, the author of the help page can markup parts of the examples for two exception rules

`dontrun`
  encloses code that should not be run.
`dontshow`
  encloses code that is invisible on help pages, but will be run both by the package checking tools, and the `example()` function. This was previously `testonly`, and that form is still accepted.

### Value

(the value of the last evaluated expression).

### Note

The examples can be many small files. On some file systems it is desirable to save space, and the files in the ‘`R-ex`’ directory of an installed package can be zipped up as a zip archive ‘`Rex.zip`’.

### Author(s)

Martin Maechler and others

### See Also

`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

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