R: Loading and Listing of Packages

Loading and Listing of Packages

Usage

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

.First.lib(libname, pkgname)

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

Arguments

`name, 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 `name` 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.
`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.
`all.available`	logical; if `TRUE` return `character` vector of all available packages in `lib.loc`.

Description

library(name) and require(name) both load the package named name. provide allows code to register services that it provides.

.First.lib() is called when a package is loaded by library(). .packages() and the .xxx variables return information about package availability.

Details

library(name) and require(name) both load the package with name name. 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 name 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. For example, the spline functions ns, bs and so on are not included in the R distribution. A package containing these functions can use provide(splines) to register this fact. Another package that needs the functions can execute require(splines) rather than library(splines) to load the spline package only if their functionality is not already available.

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

library(help = name) prints information on the package name, 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.

.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 RHOME. .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 RLIBS, which should be a colon-separated list of directories at which R library trees are rooted, and .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.

Creating Packages

Packages provide a mechanism for loading optional code and attached documentation as needed. The R distribution provides the example packages eda, mva, and stepfun.

A package consists of a subdirectory containing the files `DESCRIPTION', `INDEX', and `TITLE', and the subdirectories `R', `data', `exec', `man', and `src' (some of which can be missing).

The `DESCRIPTION' file contains information about authors, version, copyright, etc., and looks like

Package:
Version:
Author:
Description:
Depends:
License:

Continuation lines (e.g., for descriptions longer than one line) start with a whitespace character. The license field should contain an explicit statement or a well-known abbreviation (such as `GPL', `LGPL', `BSD' and `Artistic'), maybe followed by a reference to the actual license file. It is very important that this information is included—otherwise, it may not even be legally correct for others to distribute copies of the package.

The `TITLE' file contains a line giving the name of the package and a brief description. `INDEX' contains a line for each sufficiently interesting object in the package, giving its name and a description (functions such as print methods not usually called explicitly might not be included). Note that you can automatically create this file using the Rdindex program in `RHOME/etc', provided that Perl is available on your system.

The `R' subdirectory contains R code files. The code files to be installed must start with a (lower- or uppercase) letter and have one of the extensions `.R', `.S', `.q', `.r', or `.s'. We recommend using `.R', as this extension seems to be not used by any other software. If necessary, one of these files (historically `zzz.R') should use library.dynam() inside .First.lib() to load compiled code.

The `man' subdirectory should contain R documentation files for the objects in the package. The documentation files to be installed must also start with a (lower- or uppercase) letter and have the extension `.Rd' (the default) or `.rd'.

Source and a Makefile for the compiled code is in `src', containing C, FORTRAN, or Ratfor source. The Makefile will be passed various machine-dependent compile and link flags, examples of which can be seen in the eda package.

The `data' subdirectory is for additional data files the package makes available for loading using data(). Currently, data files can have one of three types as indicated by their extension: plain R code (`.R' or `.r'), tables (`.tab', `.txt', or `.csv'), or save() images (`.RData' or `.rda'). See the documentation for data() for more information. If there is a `data' subdirectory it should contain a `00Index' file that describes the datasets available.

Finally, `exec' could contain additional executables the package needs, typically Shell or Perl scripts. This mechanism is currently not used by any package, and still experimental.

Author(s)

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

[Package Contents]