library                 package:base                 R Documentation

_L_o_a_d_i_n_g _a_n_d _L_i_s_t_i_n_g _o_f _P_a_c_k_a_g_e_s

_D_e_s_c_r_i_p_t_i_o_n:

     `library' and `require' load add-on packages. `.First.lib' is
     called when a package is loaded; `.Last.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. `.find.package' returns the directory
     paths of installed packages.

_U_s_a_g_e:

     library(package, help = NULL, lib.loc = .lib.loc,
             character.only = FALSE, logical.return = FALSE,
             warn.conflicts = TRUE, keep.source = getOption("keep.source.pkgs"))
     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 = .lib.loc)
     .path.package(package = .packages(), quiet = FALSE)
     .find.package(package, lib.loc = .lib.loc, use.attached, quiet = FALSE)
     .lib.loc
     .Library
     .Autoloaded

_A_r_g_u_m_e_n_t_s:

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.

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 `options(keep.source = *)'.

 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.

_D_e_t_a_i_l_s:

     `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
     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 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
     `pos.to.env(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.

     `.find.package' returns the paths to the locations where the names
     packages can be found.  If `lib.loc' is not given or
     `use.attached' is `TRUE', 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.  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'.
     `.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' (which should be a colon-separated
     list of directories at which R library trees are rooted) followed
     by `.Library'.

_V_a_l_u_e:

     `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.

_A_u_t_h_o_r(_s):

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

_S_e_e _A_l_s_o:

     `attach', `detach', `search', `objects', `autoload',
     `library.dynam', `data', `install.packages', `INSTALL', `REMOVE'.

_E_x_a_m_p_l_e_s:

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

     .lib.loc
     .Library == .lib.loc[length(.lib.loc)]  # `by definition'

     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)
     }

