From: Philippe Grosjean (phgrosjean@sciviews.org)
Date: Fri 27 Jun 2003 - 16:34:40 EST
Message-id: <MABBLJDICACNFOLGIHJOEEBEDJAA.phgrosjean@sciviews.org>
Prof. Brian Ripley wrote:
>Philippe,
>as.list(NULL) is the same as list(), and that is what I think you should
>be using in both cases.
OK, thank you.
>However, I do think that either both or neither of your examples should
>work: my preference would be `neither' but as S allows both it should be
>`either'.
I agree with you, including on the fact that 'neither' should work. I would
prefer a language that obliges to declare list components before using them.
Experimenting a little bit more around this problem, I got that:
- assigning NULL to a list entry deletes this entry from the list. OK, fine.
Asking for:
my.list$non.existing.item gives NULL. Thus, it is consistent. However, if I
use this:
> a <- list(item1=NULL, item2=NULL)
> a
$item1
NULL
$item2
NULL
- this is a strange behaviour because the previous command should have
returned 'list()' in a. Consequently, when I reallocate NULL to either
'item1', or 'item2' of 'a', it deletes it:
> a$item1 <- NULL
> a
$item2
NULL
Not an harmfull behaviour, but inconsistent with the rest.
Best,
Philippe Grosjean
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