It is a bug that has been present in R since at least R-2.14.0 (the oldest that I have installed on my laptop).
Bill Dunlap TIBCO Software wdunlap tibco.com On Fri, Jun 19, 2020 at 10:37 AM Rui Barradas <ruipbarra...@sapo.pt> wrote: > Hello, > > > Thanks, I hadn't thought of that. > > But, why? Is it evaluated once before assignment and a second time when > the assignment occurs? > > To trace both sample and `[<-` gives 2 calls to sample. > > > trace(sample) > trace(`[<-`) > df[sample(nrow(df), 3),]$treated <- TRUE > trace: sample(nrow(df), 3) > trace: `[<-`(`*tmp*`, sample(nrow(df), 3), , value = list(unit = c(7L, > 6L, 8L), treated = c(TRUE, TRUE, TRUE))) > trace: sample(nrow(df), 3) > > > Regards, > > Rui Barradas > > > Às 17:20 de 19/06/2020, William Dunlap escreveu: > > The first subscript argument is getting evaluated twice. > > > trace(sample) > > > set.seed(2020); df[i<-sample(10,3), ]$Treated <- TRUE > > trace: sample(10, 3) > > trace: sample(10, 3) > > > i > > [1] 1 10 4 > > > set.seed(2020); sample(10,3) > > trace: sample(10, 3) > > [1] 7 6 8 > > > sample(10,3) > > trace: sample(10, 3) > > [1] 1 10 4 > > > > Bill Dunlap > > TIBCO Software > > wdunlap tibco.com <http://tibco.com> > > > > > > On Fri, Jun 19, 2020 at 8:46 AM Rui Barradas <ruipbarra...@sapo.pt > > <mailto:ruipbarra...@sapo.pt>> wrote: > > > > Hello, > > > > I don't have an answer on the reason why this happens but it seems > > like > > a bug. Where? > > > > In which of `[<-.data.frame` or `[<-.default`? > > > > A solution is to subset and assign the vector: > > > > > > set.seed(2020) > > df2 <- data.frame(unit = 1:10) > > df2$treated <- FALSE > > > > df2$treated[sample(nrow(df2), 3)] <- TRUE > > df2 > > # unit treated > > #1 1 FALSE > > #2 2 FALSE > > #3 3 FALSE > > #4 4 FALSE > > #5 5 FALSE > > #6 6 TRUE > > #7 7 TRUE > > #8 8 TRUE > > #9 9 FALSE > > #10 10 FALSE > > > > > > Or > > > > > > set.seed(2020) > > df3 <- data.frame(unit = 1:10) > > df3$treated <- FALSE > > > > df3[sample(nrow(df3), 3), "treated"] <- TRUE > > df3 > > # result as expected > > > > > > Hope this helps, > > > > Rui Barradas > > > > > > > > Às 13:49 de 19/06/2020, Sébastien Lahaie escreveu: > > > I ran into some strange behavior in R when trying to assign a > > treatment to > > > rows in a data frame. I'm wondering whether any R experts can > > explain > > > what's going on. > > > > > > First, let's assign a treatment to 3 out of 10 rows as follows. > > > > > >> df <- data.frame(unit = 1:10) > > >> df$treated <- FALSE > > >> s <- sample(nrow(df), 3) > > >> df[s,]$treated <- TRUE > > >> df > > > unit treated > > > > > > 1 1 FALSE > > > > > > 2 2 TRUE > > > > > > 3 3 FALSE > > > > > > 4 4 FALSE > > > > > > 5 5 TRUE > > > > > > 6 6 FALSE > > > > > > 7 7 TRUE > > > > > > 8 8 FALSE > > > > > > 9 9 FALSE > > > > > > 10 10 FALSE > > > > > > This is as expected. Now we'll just skip the intermediate step > > of saving > > > the sampled indices, and apply the treatment directly as follows. > > > > > >> df <- data.frame(unit = 1:10) > > >> df$treated <- FALSE > > >> df[sample(nrow(df), 3),]$treated <- TRUE > > >> df > > > unit treated > > > > > > 1 6 TRUE > > > > > > 2 2 FALSE > > > > > > 3 3 FALSE > > > > > > 4 9 TRUE > > > > > > 5 5 FALSE > > > > > > 6 6 FALSE > > > > > > 7 7 FALSE > > > > > > 8 5 TRUE > > > > > > 9 9 FALSE > > > > > > 10 10 FALSE > > > > > > Now the data frame still has 10 rows with 3 assigned to the > > treatment. But > > > the units are garbled. Units 1 and 4 have disappeared, for > > instance, and > > > there are duplicates for 6 and 9, one assigned to treatment and > > the other > > > to control. Why would this happen? > > > > > > Thanks, > > > Sebastien > > > > > > [[alternative HTML version deleted]] > > > > > > ______________________________________________ > > > R-help@r-project.org <mailto:R-help@r-project.org> mailing list > > -- To UNSUBSCRIBE and more, see > > > https://stat.ethz.ch/mailman/listinfo/r-help > > > PLEASE do read the posting guide > > http://www.R-project.org/posting-guide.html > > > and provide commented, minimal, self-contained, reproducible code. > > > > -- > > Este e-mail foi verificado em termos de vírus pelo software > > antivírus Avast. > > https://www.avast.com/antivirus > > > > ______________________________________________ > > R-help@r-project.org <mailto:R-help@r-project.org> mailing list -- > > To UNSUBSCRIBE and more, see > > https://stat.ethz.ch/mailman/listinfo/r-help > > PLEASE do read the posting guide > > http://www.R-project.org/posting-guide.html > > and provide commented, minimal, self-contained, reproducible code. > > > > -- > Este e-mail foi verificado em termos de vírus pelo software antivírus > Avast. > https://www.avast.com/antivirus > > [[alternative HTML version deleted]] ______________________________________________ R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.