exists {base}R Documentation

Is an Object Defined?

Description

Look for an R object of the given name.

Usage

exists(x, where = -1, envir = , frame, mode = "any", inherits = TRUE)

Arguments

x a variable name (given as a character string).
where where to look for the object (see the details section); if omitted, the function will search as if the name of the object appeared unquoted in an expression.
envir an alternative way to specify an environment to look in, but it's usually simpler to just use the where argument.
frame a frame in the calling list. Equivalent to giving where as sys.frame(frame).
mode the mode of object sought.
inherits should the enclosing frames of the environment be searched?

Details

The where argument can specify the environment in which to look for the object in any of several ways: as an integer (the position in the search list); as the character string name of an element in the search list; or as an environment (including using sys.frame to access the currently active function calls). The envir argument is an alternative way to specify an environment, but is primarily there for back compatibility.

This function looks to see if the name x has a value bound to it in the specified environment. If inherits is TRUE and a value is not found for x in the specified environment, the enclosures of the environment are searched until the name x is encountered. See environment and the ‘R Language Definition’ manual for details about the structure of environments and their enclosures.

Warning: inherits=TRUE is the default behaviour for R but not for S.

If mode is specified then only objects of that mode are sought. The mode may specify collections such as "numeric" and "function": any member of the collection will suffice.

Value

Logical, true if and only if an object of the correct name and mode is found.

References

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

See Also

get.

Examples

##  Define a substitute function if necessary:
if(!exists("some.fun", mode="function"))
  some.fun <- function(x) { cat("some.fun(x)\n"); x }
search()
exists("ls", 2) # true even though ls is in pos=3
exists("ls", 2, inherits = FALSE) # false

[Package base version 2.1.0 Index]