library {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.

### Usage

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

    require(package, lib.loc = NULL, quietly = FALSE, warn.conflicts = TRUE,
            keep.source = getOption("keep.source.pkgs"),
            character.only = FALSE, version, save = TRUE)

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

### 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 package. Note that `.First.lib` may attach other packages, and `pos` is computed after `.First.lib` has been run. 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. Non-existent library trees are silently ignored.
`character.only` | a logical indicating whether `package` or `help` can be assumed to be character strings.
`version` | A character string denoting a version number of the package to be loaded, for use with versioned installs: see the section later in this document.
`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`. A conflict is a function masking a function, or a non-function masking a non-function.
`keep.source` | logical. If `TRUE`, functions “keep their source” including comments, see argument `keep.source` to `options`. This applies only to the named package, and not to any packages or namespaces which might be loaded to satisfy dependencies or imports. This argument does not apply to packages using lazy-loading or saved images. Whether they have kept source is determined when they are installed (and is most likely false).
`verbose` | a logical. If `TRUE`, additional diagnostics are printed.
`quietly` | a logical. If `TRUE`, no message confirming package loading is printed.
`save` | logical or environment. If `TRUE`, a call to `require` from the source for a package will save the name of the required package in the variable `".required"`, allowing function `detach` to warn if a required package is detached. See section ‘Packages that require other packages’ below.
`libname` | a character string giving the library directory where the package was found.
`pkgname` | a character string giving the name of the package, including the version number if the package was installed with `--with-package-versions`.
`libpath` | a character string giving the complete path to the package.

### 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 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 loaded packages and do not reload a package which is already loaded.

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. Note that `installed.packages()` returns 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 loaded packages are searched before the libraries.

`.First.lib` is called when a package without a namespace is loaded by `library`. (For packages with namespaces see `.onLoad`.) 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, and with the package name including the version for a versioned install, e.g. `tree_1.0-16`). 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, but `setHook` is preferred.

`.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.)

### 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.

### Packages that require other packages

NB: This mechanism has been almost entirely superseded by using the `Depends:` field in the ‘`DESCRIPTION`’ file of a package.

The source code for a package that requires one or more other packages should have a call to `require`, preferably near the beginning of the source, and of course before any code that uses functions, classes or methods from the other package. The default for argument `save` will save the names of all required packages in the environment of the new package. The saved package names are used by `detach` when a package is detached to warn if other packages still require the to-be-detached package. Also, if a package is installed with saved image (see INSTALL), the saved package names are used to require these packages when the new package is attached.

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

### Versioned installs

Packages can be installed with version information by `R CMD INSTALL --with-package-versions` or `install.packages(installWithVers = TRUE)`. This allows more than one version of a package to be installed in a library directory, using package directory names like `foo_1.5-1`. When such packages are loaded, it is this versioned name that `search()` returns. Some utility functions require the versioned name and some the unversioned name (here `foo`).

If `version` is not specified, `library` looks first for a packages of that name, and then for versioned installs of the package, selecting the one with the latest version number. If `version` is specified, a versioned install with an exactly matching version is looked for.

If `version` is not specified, `require` will accept any version that is already loaded, whereas `library` will look for an unversioned install even if a versioned install is already loaded.

Loading more than one version of a package into an R session is not currently supported. Support for versioned installs is patchy.

### Note

`library` and `require` can only load 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.

As of version 2.0.0, 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 MS Windows.

### 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`, `library.dynam`, `data`, `install.packages` and `installed.packages`; `INSTALL`, `REMOVE`.

### Examples

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

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

[Package base version 2.3.1 Index]