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Is a Variable Defined?

Syntax

exists(x, where =NULL, envir=sys.frame(sys.parent()), frame =NULL,
       mode = "any", inherits = TRUE)

Arguments

x a variable name (given as a quoted string).
where, envir, frame an environent to be searched. By default this is the environment where the call to envir takes place.
mode the type of interest for the object.
inherits should the enclosing frames of the environment be inspected.

Description

This function looks to see if the name x has a value bound to it. If inherits is TRUE and a value is not found for x, then the parent frames of envir are searched until the name x is encountered. If mode is specified then only objects of that mode are sought. The function returns TRUE if the variable is encountered and FALSE if not.

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 }