2010/2/24 Luca Beltrame <luca.beltr...@unifi.it>:
> Hello,
>
> thanks from the help on this ML, porting is going on fast. However I've
> again(!) stumbled upon something that is not very evident (at least to me):
> null results.
>
> In R, accessing non existent items from a list yields a NULL result, and since
> some of the methods I use can or can not return something, I check for the
> result using is.null().
>
> Simple use case
>
> test_list <- list(a="some_value", b="other_value")
>
> test_list[["c"]]
> NULL
>
> However, rpy2 returns a RObject which is not None (obviously) but can't be
> tested for such a thing, unless I do:
>
> importr("base")
> base.is_null(test_list.rx2("c"))
> True
>
> Is there another way to go around this problem or should I stick with this
> solution for now?
For now, you may have to stick with that or with
from rpy2.rinterface import R_NilValue
NULL = R_NilValue
test_list.rx2("c").rsame(NULL)
The plan is to have a singleton of type RNULL (or similar), which
would let one do:
test_list.rx2("c") is RNULL
There is something similar in place for NAs (unfortunately not
extremely stable until 2.1beta).
Laurent
> Thanks.
>
> --
> Luca Beltrame, Ph.D. - luca.beltr...@unifi.it
> Post-doctoral research fellow - Duccio Cavalieri group
> Department of Pharmacology, University of Firenze
>
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