Thanks. 'by' is implemented by tapply, and it seems to behave rather erratically for empty inputs:
> FUN = function(x) x[1,] > FUNx <- function(x) FUN(df[x, , drop = FALSE]) > tapply(seq_len(10), df$b, FUNx) %>% storage.mode # array > tapply(seq_len(0), c(), FUNx) %>% storage.mode # logical > tapply(seq_len(0), c(), NULL) %>% storage.mode # integer I think this warrants a fix, strictly in the tapply R code. WDYT? On Wed, 17 Nov 2021 at 01:31, Kevin Ushey <kevinus...@gmail.com> wrote: > You can see this a bit more clearly with e.g. > > > storage.mode(byy) > [1] "list" > > storage.mode(byy.empty) > [1] "logical" > > So even though both objects have S3 class "by", they have a different > underlying internal storage mode (as simplifying the result of 'by' > has given you a 0-length logical, instead of a 0-length list). > > Best, > Kevin > > On Tue, Nov 16, 2021 at 10:21 AM Bill Dunlap <williamwdun...@gmail.com> > wrote: > > > > Try adding simplify=FALSE to the call to by(). > > > > -Bill > > > > On Tue, Nov 16, 2021 at 4:04 AM Ofek Shilon <ofekshi...@gmail.com> > wrote: > > > > > Take this toy code: > > > df <- data.frame(a=seq(10), b=rep(1:2, 5)) > > > df.empty <- subset(df, a>10) > > > byy <- by(data=df, INDICES=df$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 > [[alternative HTML version deleted]] ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
