Problems accessing environment() in function

Hi all,

I am trying to create a list of all variable/value combinations in
environment().

When a function with unset arguments is called, the method I have been
using fails with a "missing argument" error. However it should be
possible to simply skip these missing objects in the generation of the
list?

Could anyone recommend me a better way (that does not use a slow
for/eval-combination) to achieve the desired effect?

You can easily reproduce my problem using this code:

------------------------------

test1 <- function(a, b, c)
{
x <- as.list(environment())
print ("hi from test1!")
test2(a = a, b = b, c = c)

}

test2 <- function(a, b, c)
{
# PROBLEM: Why can't I get a list as in test1() here?
x <- as.list(environment())
print ("hi from test2!")
}

test1()

------------------------------

I want my list "x" in test2() to work behave just like "x" in test1().
(In this example the correct list in test2() would be empty).

Thanks a lot for your time.

Best wishes,
Heiko Neuhaus

------------------------------

test1 <- function(a, b, c)
{
x <- as.list(environment())
print ("hi from test1!")
test2(a = a, b = b, c = c)

You are rying to pass a, b, c here and hence R tries to insert those
into the environment of test2 once it is called, you have not passed
arguments to your test1 call.

Uwe Ligges

Thanks a lot for your answer!

 ------------------------------

 test1<- function(a, b, c)
 {
 x<- as.list(environment())
 print ("hi from test1!")
 test2(a = a, b = b, c = c)

 You are rying to pass a, b, c here and hence R tries to insert those
 into the environment of test2 once it is called, you have not passed
 arguments to your test1 call.

 Uwe Ligges

I am aware that I am passing non existing arguments here, which is why
my method of creating a list of the environment "as.list(environment())"
seems to fail in this case.

What I need is a way to just skip non existing objects when I create my
list. In my given example I was intending to receive an empty list,
since no valid arguments were passed to test2().

In other words: I want a list containing all _existing_ variable/value
combinations and just skip the missing ones.

f <- function(a,b,c) {
names <- ls(environment()) # get all the names
result <- list()
for (n in names) {
if (!do.call(missing, list(as.name(n))))
result[n] <- get(n)
}
result
}

If you put the ls() call later, you'll pick up other local variables
(names, result, n) as well.

Thank you very much for your suggestion.

f<- function(a,b,c) {
names<- ls(environment()) # get all the names
result<- list()
for (n in names) {
if (!do.call(missing, list(as.name(n))))
result[n]<- get(n)
}
result
}

I have already figured out a very similar solution using for/eval that
basically does the same. I was hoping that I would somehow could get
around the ugly loop using a more elegant approach.

a negative impact on performance since my function is using a lot of
parameters. I was hoping, that there was some flag to tell the as.list
function to ignore non existing objects. If that is not possible I will
have to accept this.

If you put the ls() call later, you'll pick up other local variables
(names, result, n) as well.

Of course. That is why I call it at the very first line of my function.