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 <williamwdun...@gmail.com> wrote: > > Try adding simplify=FALSE to the call to by(). > > -Bill > > On Tue, Nov 16, 2021 at 4:04 AM Ofek Shilon <ofekshi...@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? > > > > [[alternative HTML version deleted]] > > > > ______________________________________________ > > R-devel@r-project.org mailing list > > https://stat.ethz.ch/mailman/listinfo/r-devel > > > > [[alternative HTML version deleted]] > > ______________________________________________ > R-devel@r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-devel ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel