[Rd] possible bug: NULL equality in lists.

[Seth Falcon]

Uwe Ligges <ligges at statistik.uni-dortmund.de> writes:
>> Point taken, but is the behavior of as.character correct?
>> as.character(list(NULL))
>> as.character(NULL)
>
>
> I thought about it quite a while. I think the current bahaviour is
> quite OK. What should as.character do in the follwing case:
>    as.character(list("A", NA, NULL))
> ?
>
> Note that it only can return a character vector...!
>
> So, should it return a character vector of length 2? That's a bad
> idea, if the length is reduced.

But consistent with vectorizing a list using unlist:

unlist(list(NULL, NULL, "a"))
[1] "a"

> Moreover, as.character() does not get a NA or a NULL object for
> coercion but an element of type list that itself conatins NA or
> NULL...

In the case of NA, I think converting to "NA" should be a last
resort.  Since NA is a perfectly valid element of a character vector,
it would seem to be a better choice.