On Oct 7, 2010, at 7:27 PM, Eli Holmes wrote:
I'm trying to test for the existence of an object within a function,
but despite searching the help files and R-list, I can't figure out
how to do it.
Here is some test code:
#-------------------------
a=1 #now I have a in the global environment
tst <- function(a,b=1) {
# but a is not in the local function environment
print(exists("a", inherits=FALSE)) #This is how I think I should be
able to test if it is in the local function environment
print(a)
}
tst()
#----------------------
#Here's the output
[1] TRUE
Error in print(a) : argument "a" is missing, with no default
It says TRUE, even though I specified inherits=FALSE and "a" is not in
the function environment.
Yes it is, or at least its name is known, even if it doesn't have a
value:
a=1 #now I have a in the global environment
tst2 <- function(a,b=1) {
# but a is not in the local function environment
print(ls())
}
tst2()
[1] "a" "b"
tst3 <- function(a,b=1) {
# but a is not in the local function environment
print(formals("tst3"))
} ; tst3()
$a
$b
[1] 1
I've tried to pass in where and envir
arguments to exists() but I haven't been able to solve the problem.
Exactly what IS the problem? If you tested for "d" there would be a
FALSE return. And does this solve it....
> tst4 <- function(a,b=1,d=missing(a)) {
+ print(d)
+ } ; tst4()
[1] TRUE
> tst4 <- function(a,b=1,d=missing(a)) {
+ print(d)
+ } ; tst4(2)
[1] FALSE
--
David Winsemius, MD
West Hartford, CT
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