On Wed, Jan 07 2015, Milan Bouchet-Valat <nalimi...@club.fr> wrote: > Le mercredi 07 janvier 2015 à 04:25 -0800, ele...@gmail.com a écrit : >> A Nullable is immutable, its value isn't down the back of the couch >> (which is my understanding of epistemological missingness, usually >> applied to the TV remote :), it can never get a value once its null. > That's not a technical question (immutable/mutable), but a conceptual > one. If you have missing values in e.g. survey data, it usually means > that the individual has not replied to the question (away, refused to > reply, bug in the collect...). So you cannot say whether the value would > have been 3 or something else.
IMO it is very difficult to come up with a set of rules for operations on missing data that satisfies all users (and uses), mostly because "epistemological" and "ontological" missingness is sometimes mixed in the same program/library, occasionally in subtle ways. When a first best solution is not possible, my preference is for simplicity, which in this case means having a simple mental model of how missingness works. If I understand Nullable correctly, there is one simple rule to grok: "missingness propagates" -- that's it. I find this appealing, even if I have to work around some corner cases. My understanding is that R is based on the same principle with respect to NA, and it seems to work out (and, at the same time, is occasionally confusing to newbies, but that may be inevitable). best, Tamas
