[Rd] na.omit inconsistent with is.na on list

[Hugh Parsonage]

The data.frame method deliberately skips non-atomic columns before
invoking is.na(x) so I think it is fair to assume this behaviour is
intentional and assumed.

Not so clear to me that there is a sensible answer for list columns.
(List columns seem to collide with the expectation that in each
variable every observation will be of the same type)

Consider your list L as

L <- list(NULL, NA, c(NA, NA))

Seems like every observation could have a claim to be 'missing' here.
Concretely, if a data.frame had a list column representing the lat-lon
of an observation, we might only be able to represent missing values
like c(NA, NA).

On Fri, 13 Aug 2021 at 17:27, Iñaki Ucar <iucar using fedoraproject.org> wrote:
>
> On Thu, 12 Aug 2021 at 22:20, Gabriel Becker <gabembecker using gmail.com> wrote:
> >
> > Hi Toby,
> >
> > This definitely appears intentional, the first  expression of
> > stats:::na.omit.default is
> >
> >    if (!is.atomic(object))
> >
> >         return(object)
>
> I don't follow your point. This only means that the *default* method
> is not intended for non-atomic cases, but it doesn't mean it shouldn't
> exist a method for lists.
>
> > So it is explicitly just returning the object in non-atomic cases, which
> > includes lists. I was not involved in this decision (obviously) but my
> > guess is that it is due to the fact that what constitutes an observation
> > "being complete" in unclear in the list case. What should
> >
> > na.omit(list(5, NA, c(NA, 5)))
> >
> > return? Just the first element, or the first and the last? It seems, at
> > least to me, unclear. A small change to the documentation to to add "atomic
>
> > is.na(list(5, NA, c(NA, 5)))
> [1] FALSE  TRUE FALSE
>
> Following Toby's argument, it's clear to me: the first and the last.
>
> Iñaki
>
> > (in the sense of is.atomic returning \code{TRUE})" in front of "vectors"
> > or similar  where what types of objects are supported seems justified,
> > though, imho, as the current documentation is either ambiguous or
> > technically incorrect, depending on what we take "vector" to mean.
> >
> > Best,
> > ~G
> >
> > On Wed, Aug 11, 2021 at 10:16 PM Toby Hocking <tdhock5 using gmail.com> wrote:
> >
> > > Also, the na.omit method for data.frame with list column seems to be
> > > inconsistent with is.na,
> > >
> > > > L <- list(NULL, NA, 0)
> > > > str(f <- data.frame(I(L)))
> > > 'data.frame': 3 obs. of  1 variable:
> > >  $ L:List of 3
> > >   ..$ : NULL
> > >   ..$ : logi NA
> > >   ..$ : num 0
> > >   ..- attr(*, "class")= chr "AsIs"
> > > > is.na(f)
> > >          L
> > > [1,] FALSE
> > > [2,]  TRUE
> > > [3,] FALSE
> > > > na.omit(f)
> > >    L
> > > 1
> > > 2 NA
> > > 3  0
> > >
> > > On Wed, Aug 11, 2021 at 9:58 PM Toby Hocking <tdhock5 using gmail.com> wrote:
> > >
> > > > na.omit is documented as "na.omit returns the object with incomplete
> > > cases
> > > > removed." and "At present these will handle vectors," so I expected that
> > > > when it is used on a list, it should return the same thing as if we
> > > subset
> > > > via is.na; however I observed the following,
> > > >
> > > > > L <- list(NULL, NA, 0)
> > > > > str(L[!is.na(L)])
> > > > List of 2
> > > >  $ : NULL
> > > >  $ : num 0
> > > > > str(na.omit(L))
> > > > List of 3
> > > >  $ : NULL
> > > >  $ : logi NA
> > > >  $ : num 0
> > > >
> > > > Should na.omit be fixed so that it returns a result that is consistent
> > > > with is.na? I assume that is.na is the canonical definition of what
> > > > should be considered a missing value in R.
> > > >
> > >
> > >         [[alternative HTML version deleted]]
> > >
> > > ______________________________________________
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> > > https://stat.ethz.ch/mailman/listinfo/r-devel
> > >
> >
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> >
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>
>
>
> --
> Iñaki Úcar
>
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