The first subscript argument is getting evaluated twice. > trace(sample) > set.seed(2020); df[i<-sample(10,3), ]$Treated <- TRUE trace: sample(10, 3) trace: sample(10, 3) > i [1] 1 10 4 > set.seed(2020); sample(10,3) trace: sample(10, 3) [1] 7 6 8 > sample(10,3) trace: sample(10, 3) [1] 1 10 4
Bill Dunlap TIBCO Software wdunlap tibco.com On Fri, Jun 19, 2020 at 8:46 AM Rui Barradas <ruipbarra...@sapo.pt> wrote: > Hello, > > I don't have an answer on the reason why this happens but it seems like > a bug. Where? > > In which of `[<-.data.frame` or `[<-.default`? > > A solution is to subset and assign the vector: > > > set.seed(2020) > df2 <- data.frame(unit = 1:10) > df2$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 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 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. > [[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.