| library {base} | R Documentation |
library and require load add-on packages.
.First.lib is called when a package is loaded;
.Last.lib is called when a package is detached.
library(package, help, pos = 2, lib.loc = NULL,
character.only = FALSE, logical.return = FALSE,
warn.conflicts = TRUE,
keep.source = getOption("keep.source.pkgs"),
verbose = getOption("verbose"),
version)
require(package, quietly = FALSE, warn.conflicts = TRUE,
keep.source = getOption("keep.source.pkgs"),
character.only = FALSE, version, save = TRUE)
.First.lib(libname, pkgname)
.Last.lib(libpath)
package, help |
the name of a package, given as a name or
literal character string, or a character string, depending on
whether character.only is FALSE (default) or
TRUE). |
pos |
the position on the search list at which to attach the
loaded package. Note that .First.lib may attach other
packages, and pos is computed after .First.lib
has been run. Can also be the name of a position on the current
search list as given by search(). |
lib.loc |
a character vector describing the location of R
library trees to search through, or NULL. The default value
of NULL corresponds to all libraries currently known.
Non-existent library trees are silently ignored. |
character.only |
a logical indicating whether package or
help can be assumed to be character strings. |
version |
A character string denoting a version number of the package to be loaded, for use with versioned installs: see the section later in this document. |
logical.return |
logical. If it is TRUE, FALSE or
TRUE is returned to indicate success. |
warn.conflicts |
logical. If TRUE, warnings are
printed about conflicts from attaching the new
package, unless that package contains an object .conflicts.OK. |
keep.source |
logical. If TRUE, functions
“keep their source” including comments, see argument
keep.source to options. This applies only to
the named package, and not to any packages or namespaces which might be
loaded to satisfy dependencies or imports.
This argument does not apply to packages using lazy-loading or saved images. Whether they have kept source is determined when they are installed (and is most likely false). |
verbose |
a logical. If TRUE, additional diagnostics are
printed. |
quietly |
a logical. If TRUE, no message confirming
package loading is printed. |
save |
logical or environment. If TRUE, a call to
require from the source for a package will save the name of
the required package in the variable ".required", allowing
function detach to warn if a required package is
detached. See section ‘Packages that require other packages’ below. |
libname |
a character string giving the library directory where the package was found. |
pkgname |
a character string giving the name of the package,
including the version number if the package was installed with
--with-package-versions. |
libpath |
a character string giving the complete path to the package. |
library(package) and require(package) both load the
package with name package. require is designed for use
inside other functions; it returns FALSE and gives a warning
(rather than an error as library() does by default) if the
package does not exist. Both functions check and update the list of
currently loaded packages and do not reload a package which is already
loaded.
If library is called with no package or help
argument, it lists all available packages in the libraries specified
by lib.loc, and returns the corresponding information in an
object of class "libraryIQR". The structure of this class may
change in future versions. In earlier versions of R, only the names
of all available packages were returned; use .packages(all =
TRUE) for obtaining these. Note that
installed.packages()
returns even more information.
library(help = somename) computes basic information about the
package somename, and returns this in an object of class
"packageInfo". The structure of this class may change in
future versions. When used with the default value (NULL) for
lib.loc, the loaded packages are searched before the libraries.
.First.lib is called when a package without a namespace is
loaded by library. (For packages with namespaces see
.onLoad.) It is called with two arguments, the name of
the library directory where the package was found (i.e., the
corresponding element of lib.loc), and the name of the package
(in that order, and with the package name including the version for a
versioned install, e.g. tree_1.0-16). It is a good place to
put calls to library.dynam which are needed when loading
a package into this function (don't call library.dynam
directly, as this will not work if the package is not installed in a
“standard” location). .First.lib is invoked after the
search path interrogated by search() has been updated, so
as.environment(match("package:name", search())) will return the
environment in which the package is stored. If calling
.First.lib gives an error the loading of the package is
abandoned, and the package will be unavailable. Similarly, if the
option ".First.lib" has a list element with the package's name,
this element is called in the same manner as .First.lib when
the package is loaded. This mechanism allows the user to set package
“load hooks” in addition to startup code as provided by the
package maintainers, but setHook is preferred.
.Last.lib is called when a package is detached. Beware
that it might be called if .First.lib has failed, so it
should be written defensively. (It is called within try,
so errors will not stop the package being detached.)
library returns the list of loaded (or available) packages
(or TRUE if logical.return is TRUE).
require returns a logical indicating whether the required
package is available.
NB: This mechanism has been almost entirely superseded by
using the Depends: field in the ‘DESCRIPTION’ file of a package.
The source code for a
package that requires one or more other packages should have a call
to require, preferably near the beginning of the source, and
of course before any code that uses functions, classes or methods
from the other package. The default for argument save will
save the names of all required packages in the environment of the
new package. The saved package names are used by
detach when a package is detached to warn if other
packages still require the to-be-detached package. Also, if a package is
installed with saved image (see INSTALL), the saved package
names are used to require these packages when the new package is
attached.
library takes some further actions when package methods
is attached (as it is by default). Packages may define formal generic
functions as well as re-defining functions in other packages (notably
base) to be generic, and this information is cached whenever
such a package is loaded after methods and re-defined functions
are excluded from the list of conflicts. The check requires looking
for a pattern of objects; the pattern search may be avoided by
defining an object .noGenerics
(with any value) in the package. Naturally, if the package
does have any such methods, this will prevent them from being used.
Packages can be installed with version information by R CMD
INSTALL --with-package-versions or
install.packages(installWithVers = TRUE). This allows
more than one version of a package to be installed in a library
directory, using package directory names like foo_1.5-1. When
such packages are loaded, it is this versioned name
that search() returns. Some utility functions require
the versioned name and some the unversioned name (here foo).
If version is not specified, library looks first
for a packages of that name, and then for versioned installs of the
package, selecting the one with the latest version number. If
version is specified, a versioned install with an
exactly matching version is looked for.
If version is not specified, require will accept any
version that is already loaded, whereas library will look for
an unversioned install even if a versioned install is already loaded.
Loading more than one version of a package into an R session is not currently supported. Support for versioned installs is patchy.
library and require can only load an installed
package, and this is detected by having a ‘DESCRIPTION’ file
containing a Built: field.
Under Unix-alikes, the code checks that the package was installed
under a similar operating system as given by R.version$platform
(the canonical name of the platform under which R was compiled),
provided it contains compiled code. Packages which do not contain
compiled code can be shared between Unix-alikes, but not to other OSes
because of potential problems with line endings and OS-specific help
files.
As of version 2.0.0, the package name given to library and
require must match the name given in the package's
DESCRIPTION file exactly, even on case-insensitive file systems
such as MS Windows.
Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) The New S Language. Wadsworth & Brooks/Cole.
attach, detach, search,
objects, autoload,
library.dynam, data,
install.packages and
installed.packages;
INSTALL, REMOVE.
library() # list all available packages
library(lib = .Library) # list all packages in the default library
library(help = splines) # documentation on package 'splines'
library(splines) # load package 'splines'
require(splines) # the same
search() # "splines", too
detach("package:splines")
# if the package name is in a character vector, use
pkg <- "splines"
library(pkg, character.only = TRUE)
detach(pos = match(paste("package", pkg, sep=":"), search()))
require(pkg, character.only = TRUE)
detach(pos = match(paste("package", pkg, sep=":"), search()))
require(nonexistent) # FALSE
## Not run:
## Suppose a package needs to call a shared library named 'fooEXT',
## where 'EXT' is the system-specific extension. Then you should use
.First.lib <- function(lib, pkg) {
library.dynam("foo", pkg, lib)
}
## if you want to mask as little as possible, use
library(mypkg, pos = "package:base")
## End(Not run)