Vitalie Spinu wrote:
On Fri, Oct 8, 2010 at 7:49 PM, Duncan Murdoch <murdoch.dun...@gmail.com>wrote:
On 08/10/2010 12:24 PM, Vitalie Spinu wrote:
On Fri, Oct 8, 2010 at 12:14 PM, Duncan Murdoch<murdoch.dun...@gmail.com
wrote:
Vitalie Spinu wrote:
Hello Everyone!
NULL replacement will change expression object into list:
te<- expression(a=23*4, b=33-2)
te
expression(a = 23 * 4, b = 33 - 2)
te[["a"]]<- quote(blabla) #ok
te
expression(a = blabla, b = 33 - 2)
te[["a"]]<- NULL #change to list
te
$b
33 - 2
I am on w32, version 2.11.1 (2010-05-31)
That's certainly an inconsistency, still present in a recent R-devel
(but I
haven't checked the latest beta). I don't know if it's a bug: NULL
assignments are handled specially in other situations (e.g. if te was a
list
to start, the NULL assignment would remove the "a" entry).
A simple workaround is to use
te["a"]<- expression(NULL)
or te<- te[-1]
instead, depending on what you expected to happen.
As ussual with NULL assignment in recursive structures, I would expect to
remove the elements altogether. And this is exactly what I need.
I would say it's a bug, because NULL assignment in data.frames would not
convert them to lists, for example.
I think you're probably right.
Thanks for looking into it. It's quite inconvenient when you have to
manipulate named expression. Have to use constructs like
et<-et[!names(et)%in%"a"].
Or simply follow te["a"] <- NULL
with
te <- as.expression(te)
This is a pretty fast operation if te is an expression or a list formed by
mistaken conversion from one.
D
But is this a reliable way to do it? I have been struggling some time ago
with this type of conversion.
Can not thing of an example now. But as far as I could remember, the
conversion to list of an expression is not always reversible with
as.expression. Am I wrong?
I don't know of any examples, but this is your construction. I think
it's very unlikely this will be fixed for 2.12.0, but it will probably
be fixed for 2.12.1, if
1. There is a 2.12.1
and
2. It really isn't intentional behaviour.
Duncan Murdoch
uncan Murdoch
Vitally.
Duncan Murdoch
Regards,
Vitally.
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