Loading and Listing of Packages

Description

library and require load add-on packages; provide allows code to register services that packages provide. .First.lib is called when a package is loaded; .packages returns information about package availability. .path.package returns information about where a package was loaded from.

Usage

library(package, help = NULL, lib.loc = .lib.loc,
        character.only = FALSE, logical.return = FALSE,
        warn.conflicts = TRUE)
require(package, quietly = FALSE, warn.conflicts = TRUE)
provide(package)

.First.lib(libname, pkgname)

.packages(all.available = FALSE, lib.loc = .lib.loc)
.path.package(package = .packages())
.lib.loc
.Library
.Provided
.Autoloaded

Arguments

Details

library(package) and require(package) both load the package with name package. require is designed for use inside other functions; it returns FALSE and optionally gives a warning, rather than giving an error, if the package does not exist. Both functions check and update the list of currently loaded packages and do not reload code that is already loaded. require also checks the list .Provided.

provide allows code to register services that it provides. The argument is stored in the list .Provided. provide returns FALSE if the package was already present in .Provided or among the packages in search(). The main use for provide is when multiple packages share code. This is most likely when the code implements features present in S(-PLUS) but not in R.

If library is called with no package or help argument, it gives a list of all available packages in lib.loc and invisibly returns their names (same as .packages(all = TRUE)).

library(help = somename) prints information on the package somename, typically by listing the most important user level objects it contains.

.First.lib() is called when a package is loaded by library(). It is called with two arguments, the name of the library tree where the package was found (i.e., the corresponding element of lib.loc), and the name of the package (in that order). 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 search() has been updated, so pos.to.env(match("package:name"), search()) will return the environment in which the package is stored.

.packages() returns the ``base names'' of the currently attached packages invisibly whereas .packages(all.available = TRUE) gives (visibly) all packages available in the library location path lib.loc.

.path.package returns the paths from which the named packages were loaded, or if none were named, for all currently loaded packages. It will warn if the packages named are not loaded.

.Autoloaded contains the ``base names'' of the packages for which autoloading has been promised.

.Library is a character string giving the location of the default library, the ``library'' subdirectory of R_HOME. .lib.loc is a character vector with the locations of all library trees that R should use. It is initialized at startup from the environment variable R_LIBS (RLIBS as used by older versions of R is no longer accepted) (which should be a semicolon-separated list of directories at which R library trees are rooted) followed by .Library.

Value

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.

Author(s)

R core; Guido Masarotto for the all.available=TRUE part of .packages.

See Also

attach, detach, search, objects, autoload, library.dynam, data, install.packages.

Examples

.packages()                 # maybe just "base"
.packages(all = TRUE)       # return all available as char.vector
library()                   # list all available packages
library(lib = .Library)     # list all packages in the default library
library(help = eda)         # documentation on package "eda"
library(eda)                # load package "eda"
require(eda)                # the same
.packages()                 # "eda", too
require(nonexistent)        # FALSE
## Suppose a package needs to call a shared library named "foo.EXT",
## where "EXT" is the system-specific extension.  Then you should use
.First.lib <- function(lib, pkg) {
  library.dynam("foo", pkg, lib)
}