R: Is an Object Defined?

exists {base}

R Documentation

Is an Object Defined?

Description

Search for an R object of the given name on the search path.

Usage

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

Arguments

x

a variable name (given as a character string).

where, envir, frame

an environment 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.

Details

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. Warning: This is the default behaviour for R but not for S.

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.

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=F) # false