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detach: Detach Objects from the Search Path

detach

R Documentation

Detach Objects from the Search Path

Description

Detach a database, i.e., remove it from the search() path of available R objects. Usually this is either a data.frame which has been attached or a package which was attached by library.

Usage

detach(name, pos = 2L, unload = FALSE, character.only = FALSE,
       force = FALSE)

Arguments

`name`	The object to detach. Defaults to `search()[pos]`. This can be an unquoted name or a character string but not a character vector. If a number is supplied this is taken as `pos`.
`pos`	Index position in `search()` of the database to detach. When `name` is a number, `pos = name` is used.
`unload`	A logical value indicating whether or not to attempt to unload the namespace when a package is being detached. If the package has a namespace and `unload` is `TRUE`, then `detach` will attempt to unload the namespace via `unloadNamespace`: if the namespace is imported by another namespace or `unload` is `FALSE`, no unloading will occur.
`character.only`	a logical indicating whether `name` can be assumed to be a character string.
`force`	logical: should a package be detached even though other attached packages depend on it?

Details

This is most commonly used with a single number argument referring to a position on the search list, and can also be used with a unquoted or quoted name of an item on the search list such as package:tools.

If a package has a namespace, detaching it does not by default unload the namespace (and may not even with unload = TRUE), and detaching will not in general unload any dynamically loaded compiled code (DLLs); see getLoadedDLLs and library.dynam.unload. Further, registered S3 methods from the namespace will not be removed, and because S3 methods are not tagged to their source on registration, it is in general not possible to safely un-register the methods associated with a given package. If you use library on a package whose namespace is loaded, it attaches the exports of the already loaded namespace. So detaching and re-attaching a package may not refresh some or all components of the package, and is inadvisable. The most reliable way to completely detach a package is to restart R.

Value

The return value is invisible. It is NULL when a package is detached, otherwise the environment which was returned by attach when the object was attached (incorporating any changes since it was attached).

Good practice

detach() without an argument removes the first item on the search path after the workspace. It is all too easy to call it too many or too few times, or to not notice that the search path has changed since an attach call.

Use of attach/detach is best avoided in functions (see the help for attach) and in interactive use and scripts it is prudent to detach by name.

Note

You cannot detach either the workspace (position 1) nor the base package (the last item in the search list), and attempting to do so will throw an error.

Unloading some namespaces has undesirable side effects: e.g. unloading grid closes all graphics devices, and on some systems tcltk cannot be reloaded once it has been unloaded and may crash R if this is attempted.

References

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

Examples

require(splines) # package
detach(package:splines)
## or also
library(splines)
pkg <- "package:splines"

detach(pkg, character.only = TRUE)

## careful: do not do this unless 'splines' is not already attached.
library(splines)
detach(2) # 'pos' used for 'name'

## an example of the name argument to attach
## and of detaching a database named by a character vector
attach_and_detach <- function(db, pos = 2)
{
   name <- deparse1(substitute(db))
   attach(db, pos = pos, name = name)
   print(search()[pos])
   detach(name, character.only = TRUE)
}
attach_and_detach(women, pos = 3)