R: Loading and Listing of Packages

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. `.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.

### Usage

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

    .Library
    .Autoloaded

### Arguments

`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, or `NULL`. The default value of `NULL` corresponds to all libraries currently known.
`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 argument `keep.source` to `options`.
`verbose` | a logical. If `TRUE`, additional diagnostics are printed.
`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.
`new` | a character vector with the locations of R library trees.

### 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 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 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.

`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 `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.

`.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. This function is not meant to be called by users, and its interface might change in future versions.

`.find.package` returns the paths to the locations where the given packages can be found. If `lib.loc` is `NULL`, then 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. If `verbose` is true, warnings about packages found more than once are given. Argument `use.attached` is deprecated. 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`. `.libPaths` is used for getting or setting the library trees that R knows about (and hence uses when looking for packages). If called with argument `new`, the library search path is set to `unique(new, .Library)` and this is returned. If given no argument, a character vector with the currently known library trees is returned. The library search path 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) by calling `.libPaths` with the directories specified in `R_LIBS`. Currently, the global variable `.lib.loc` is used for storing the paths to the known library trees; however, this variable should not be accessed directly.

### 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.

### Author(s)

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

### See Also

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

### Examples

    (.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
    detach("package:eda")

    # if the package name is in a character vector, use
    pkg <- "eda"
    library(pkg, character.only = TRUE)
    detach(pos = match(paste("package", pkg, sep=":"), search()))

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

    .libPaths()                 # all library trees R knows about

    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)
    }

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