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, quietly = FALSE,
        verbose = getOption("verbose"),
        mask.ok, exclude, include.only,
        attach.required = missing(include.only))

require(package, lib.loc = NULL, quietly = FALSE,
        warn.conflicts,
        character.only = FALSE,
        mask.ok, exclude, include.only,
        attach.required = missing(include.only))

conflictRules(pkg, mask.ok = NULL, exclude = NULL)

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. The default is TRUE unless specified as FALSE in the conflicts.policy option.
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.
pkg	character string naming a package.
mask.ok	character vector of names of objects that can mask objects on the search path without signaling an error when strict conflict checking is enabled
exclude,include.only	character vector of names of objects to exclude or include in the attached frame. Only one of these arguments may be used in a call to library or require.
attach.required	logical specifying whether required packages listed in the Depends clause of the DESCRIPTION file should be attached automatically.

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.

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.

Conflicts

Handling of conflicts depends on the setting of the conflicts.policy option. If this option is not set, then conflicts result in warning messages if the argument warn.conflicts is TRUE. If the option is set to the character string "strict", then all unresolved conflicts signal errors. Conflicts can be resolved using the mask.ok, exclude, and include.only arguments to library and require. Defaults for mask.ok and exclude can be specified using conflictRules.

If the conflicts.policy option is set to the string "depends.ok" then conflicts resulting from attaching declared dependencies will not produce errors, but other conflicts will. This is likely to be the best setting for most users wanting some additional protection against unexpected conflicts.

The policy can be tuned further by specifying the conflicts.policy option as a named list with the following fields:

error:

logical; if TRUE treat unresolved conflicts as errors.

warn:

logical; unless FALSE issue a warning message when conflicts are found.

generics.ok:

logical; if TRUE ignore conflicts created by defining S4 generics for functions on the search path.

depends.ok:

logical; if TRUE do not treat conflicts with required packages as errors.

can.mask:

character vector of names of packages that are allowed to be masked. These would typically be base packages attached by default.

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.

Note

library and require can only load/attach an installed package, and this is detected by having a ‘DESCRIPTION’ file containing a Built: field.

Under Unix-alikes, the code checks that the package was installed under a similar operating system as given by R.version$platform (the canonical name of the platform under which R was compiled), provided it contains compiled code. Packages which do not contain compiled code can be shared between Unix-alikes, but not to other OSes because of potential problems with line endings and OS-specific help files. If sub-architectures are used, the OS similarity is not checked since the OS used to build may differ (e.g. i386-pc-linux-gnu code can be built on an x86_64-unknown-linux-gnu OS).

The package name given to library and require must match the name given in the package's ‘DESCRIPTION’ file exactly, even on case-insensitive file systems such as are common on Windows and macOS.

References

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

See Also

.libPaths, .packages.

attach, detach, search, objects, autoload, requireNamespace, library.dynam, data, install.packages and installed.packages; INSTALL, REMOVE.

The initial set of packages attached is set by options(defaultPackages=): see also Startup.

Examples

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
## Not run: 
## if you want to mask as little as possible, use
library(mypkg, pos = "package:base")

## End(Not run)