exists(x, where =NULL, envir=sys.frame(sys.parent()), frame =NULL,
mode = "any", inherits = TRUE)
x
| a variable name (given as a quoted 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. |
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.
get.
## 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