library                 package:base                 R Documentation

Loading and Listing of Packages

Description:

     `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. `.packages' returns information about package
     availability. `.path.package' returns information about where a
     package was loaded from. `.find.package' returns the directory
     paths of installed packages.

Usage:

     library(package, help, lib.loc = NULL, character.only = FALSE,
             logical.return = FALSE, warn.conflicts = TRUE,
             keep.source = getOption("keep.source.pkgs"),
             verbose = getOption("verbose"))
     require(package, quietly = FALSE, warn.conflicts = TRUE,
             keep.source = getOption("keep.source.pkgs"))

     .First.lib(libname, pkgname)
     .Last.lib(libpath)

     .packages(all.available = FALSE, lib.loc = NULL)
     .path.package(package = .packages(), quiet = FALSE)
     .find.package(package, lib.loc = NULL, use.attached, quiet = FALSE,
                   verbose = getOption("verbose"))
     .libPaths(new)

     .Library
     .Autoloaded

Arguments:

package, help: name or character string giving the name of a package.

 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.

character.only: a logical indicating whether `package' or `help' can be
          assumed to be character strings.

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'.

 verbose: a logical.  If `TRUE', additional diagnostics are printed.

 quietly: a logical.  If `TRUE', a warning will not be printed if the
          package cannot be found.

 libname: a character string giving the library directory where the
          package was found.

 pkgname: a character string giving the name of the package.

 libpath: a character string giving the complete path to the package.

all.available: logical; if `TRUE' return a character vector of all
          available packages in `lib.loc'.

   quiet: logical. For `.path.package', should this not give warnings
          or an error if the package(s) are not loaded? For
          `.find.package', should this not give warnings or an error if
          the package(s) are not found?

use.attached: a logical indicating whether attached packages should be
          considered in addition to the ones installed in the given
          libraries.

     new: a character vector with the locations of R library trees.

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.

     For large packages, setting `keep.source = FALSE' may save quite a
     bit of memory.

     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.

     `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 directory
     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 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.

     `.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.)

     `.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. Unless `quiet = TRUE' it will warn if some of the
     packages named are not loaded, and given an error if none are. 
     This function is not meant to be called by users, and its
     interface might change in future versions.

     `.find.package' returns the paths to the locations where the given
     packages can be found.  If `lib.loc' is `NULL', then then attached
     packages are searched before the libraries.  If a package is found
     more than once, the first match is used.  Unless `quiet = TRUE' a
     warning will be given about the named packages which are not
     found, and an error if none are.  If `verbose' is true, warnings
     about packages found more than once are given. Argument
     `use.attached' is deprecated.  This function is not meant to be
     called by users, and its interface might change in future
     versions.

     `.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'.
     `.libPaths' is used for getting or setting the library trees that
     R knows about (and hence uses when looking for packages).  If
     called with argument `new', the library search path is set to
     `unique(new, .Library)' and this is returned.  If given no
     argument, a character vector with the currently known library
     trees is returned.  The library search path is initialized at
     startup from the environment variable `R_LIBS' (which should be a
     colon-separated list of directories at which R library trees are
     rooted) by calling `.libPaths' with the directories specified in
     `R_LIBS'.  Currently, the global variable `.lib.loc' is used for
     storing the paths to the known library trees; however, this
     variable should not be accessed directly.

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', `INSTALL', `REMOVE'.

Examples:

     (.packages())               # maybe just "base"
     .packages(all = TRUE)       # return all available as character 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
     detach("package:eda")

     # if the package name is in a character vector, use
     pkg <- "eda"
     library(pkg, character.only = TRUE)
     detach(pos = match(paste("package", pkg, sep=":"), search()))

     .path.package()
     .Autoloaded                 # maybe "ctest"

     .libPaths()                 # all library trees R knows about

     require(nonexistent)        # FALSE
     ## 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)
     }

