[Rd] Inconsistent is.list results on 'by' objects

[Kevin Ushey]

You can see this a bit more clearly with e.g.

> storage.mode(byy)
[1] "list"
> storage.mode(byy.empty)
[1] "logical"

So even though both objects have S3 class "by", they have a different
underlying internal storage mode (as simplifying the result of 'by'
has given you a 0-length logical, instead of a 0-length list).

Best,
Kevin

On Tue, Nov 16, 2021 at 10:21 AM Bill Dunlap <williamwdunlap using gmail.com> wrote:
>
> Try adding simplify=FALSE to the call to by().
>
> -Bill
>
> On Tue, Nov 16, 2021 at 4:04 AM Ofek Shilon <ofekshilon using gmail.com> wrote:
>
> > Take this toy code:
> > df       <- data.frame(a=seq(10), b=rep(1:2, 5))
> > df.empty <- subset(df, a>10)
> > byy       <- by(data=df,       INDICES=df$b, FUN=function(x) x[1,])
> > byy.empty <- by(data=df.empty, INDICES=df.empty$b, FUN=function(x) x[1,])
> >
> > class(byy)       # "by"
> > class(byy.empty) # "by"
> >
> > is.list(byy)        # TRUE
> > is.list(byy.empty)  # FALSE!
> >
> >
> > This behavior already messed up stuff elsewhere:
> > https://github.com/Rdatatable/data.table/issues/5258
> >
> > I'd say any questions about the class of an object (whether 'class' or
> > indirectly by 'is.**')
> > should not have the answers depend on the specific contents of the object.
> >
> > Does this qualify as an R bug? Am I missing something?
> >
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