library: Loading/Attaching and Listing of Packages

Description

library and require load and attach add-on packages.

Usage

library(package, help, pos = 2, lib.loc = NULL,
        character.only = FALSE, logical.return = FALSE,
        warn.conflicts = TRUE, quietly = FALSE,
        verbose = getOption("verbose"))
require(package, lib.loc = NULL, quietly = FALSE,
        warn.conflicts = TRUE,
        character.only = FALSE)

Arguments

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 namespace. 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 to .libPaths(). Non-existent library trees are silently ignored.

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. A conflict is a function masking a function, or a non-function masking a non-function.

verbose

a logical. If TRUE, additional diagnostics are printed.

quietly

a logical. If TRUE, no message confirming package attaching is printed, and most often, no errors/warnings are printed if package attaching fails.

Value

Normally library returns (invisibly) the list of attached packages, but TRUE or FALSE if logical.return is TRUE. When called as library() it returns an object of class "libraryIQR", and for library(help=), one of class "packageInfo".

require returns (invisibly) a logical indicating whether the required package is available.

Licenses

Some packages have restrictive licenses, and there is a mechanism to allow users to be aware of such licenses. If getOption("checkPackageLicense") == TRUE, then at first use of a package with a not-known-to-be-FOSS (see below) license the user is asked to view and accept the license: a list of accepted licenses is stored in file ~/.R/licensed. In a non-interactive session it is an error to use such a package whose license has not already been recorded as accepted.

As from R 3.4.0 the license check is done when the namespace is loaded.

Free or Open Source Software (FOSS, e.g.https://en.wikipedia.org/wiki/FOSS) packages are determined by the same filters used by available.packages but applied to just the current package, not its dependencies.

There can also be a site-wide file R_HOME/etc/licensed.site of packages (one per line).

Formal methods

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 namespace is loaded after methods and re-defined functions (implicit generics) are excluded from the list of conflicts. The caching and check for conflicts require looking for a pattern of objects; the search may be avoided by defining an object .noGenerics (with any value) in the namespace. Naturally, if the package does have any such methods, this will prevent them from being used.

Details

library(package) and require(package) both load the namespace of the package with name package and attach it on the search list. 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 attached packages and do not reload a namespace which is already loaded. (If you want to reload such a package, call detach(unload = TRUE) or unloadNamespace first.) If you want to load a package without attaching it on the search list, see requireNamespace.

To suppress messages during the loading of packages use suppressPackageStartupMessages: this will suppress all messages from R itself but not necessarily all those from package authors.

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.) Use .packages(all = TRUE) to obtain just the names of all available packages, and installed.packages() for 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 attached packages are searched before the libraries.

References

Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) The New S Language. Wadsworth & Brooks/Cole.

Examples

Run this code

library()                   # list all available packages
library(lib.loc = .Library) # list all packages in the default library
library(help = splines)     # documentation on package 'splines'
library(splines)            # attach 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

## if you want to mask as little as possible, use
library(mypkg, pos = "package:base")

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