Yes. Beating a pretty weary horse, a slightly cleaner version of my prior offering using with(), instead of within() is:
with(dat, dat[sampleNo[sample(var1[!var1%%2 & !sampleNo], 10, rep=FALSE)], "sampleNo"] <- 2) with() and within() are convenient ways to avoid having to repeatedly name the columns via $ . Note also the use of logical subscripting of the data frame in which numeric 0 is coerced to FALSE and any nonzero value to TRUE (which I should have done previously). Cheers, Bert Bert Gunter "The trouble with having an open mind is that people keep coming along and sticking things into it." -- Opus (aka Berkeley Breathed in his "Bloom County" comic strip ) On Mon, Sep 25, 2017 at 11:43 AM, Eric Berger <[email protected]> wrote: > Hi David, > I was about to post a reply when Bert responded. His answer is good > and his comment to use the name 'dat' rather than 'data' is instructive. > I am providing my suggestion as well because I think it may address > what was causing you some confusion (mainly to use "which", but also > the missing !) > > idx2 <- sample( which( (!data$var1%%2) & data$sampleNo==0 ), size=10, > replace=F) > data[idx2,]$sampleNo <- 2 > > Eric > > > > On Mon, Sep 25, 2017 at 9:03 PM, Bert Gunter <[email protected]> > wrote: > >> For personal aesthetic reasons, I changed the name "data" to "dat". >> >> Your code, with a slight modification: >> >> set.seed (1357) ## for reproducibility >> dat <- data.frame(var1=seq(1:40), var2=seq(40,1)) >> dat$sampleNo <- 0 >> idx <- sample(seq(1,nrow(dat)), size=10, replace=F) >> dat[idx,"sampleNo"] <-1 >> >> ## yielding >> > dat >> >> var1 var2 sampleNo >> 1 1 40 0 >> 2 2 39 1 >> 3 3 38 0 >> 4 4 37 0 >> 5 5 36 0 >> 6 6 35 1 >> 7 7 34 0 >> 8 8 33 0 >> 9 9 32 0 >> 10 10 31 0 >> 11 11 30 0 >> 12 12 29 0 >> 13 13 28 0 >> 14 14 27 0 >> 15 15 26 1 >> 16 16 25 1 >> 17 17 24 0 >> 18 18 23 0 >> 19 19 22 0 >> 20 20 21 1 >> 21 21 20 0 >> 22 22 19 1 >> 23 23 18 0 >> 24 24 17 1 >> 25 25 16 0 >> 26 26 15 1 >> 27 27 14 0 >> 28 28 13 0 >> 29 29 12 0 >> 30 30 11 0 >> 31 31 10 0 >> 32 32 9 0 >> 33 33 8 0 >> 34 34 7 0 >> 35 35 6 1 >> 36 36 5 0 >> 37 37 4 1 >> 38 38 3 0 >> 39 39 2 0 >> 40 40 1 0 >> >> ## This is basically a transcription of your specification into indexing >> logic >> >> dat <- within(dat,sampleNo[sample(var1[(var1%%2 == 0) & >> sampleNo==0],10,rep=FALSE)] <- 2) >> >> ##yielding >> > dat >> >> var1 var2 sampleNo >> 1 1 40 0 >> 2 2 39 1 >> 3 3 38 0 >> 4 4 37 2 >> 5 5 36 0 >> 6 6 35 1 >> 7 7 34 0 >> 8 8 33 2 >> 9 9 32 0 >> 10 10 31 2 >> 11 11 30 0 >> 12 12 29 0 >> 13 13 28 0 >> 14 14 27 2 >> 15 15 26 1 >> 16 16 25 1 >> 17 17 24 0 >> 18 18 23 2 >> 19 19 22 0 >> 20 20 21 1 >> 21 21 20 0 >> 22 22 19 1 >> 23 23 18 0 >> 24 24 17 1 >> 25 25 16 0 >> 26 26 15 1 >> 27 27 14 0 >> 28 28 13 2 >> 29 29 12 0 >> 30 30 11 2 >> 31 31 10 0 >> 32 32 9 2 >> 33 33 8 0 >> 34 34 7 2 >> 35 35 6 1 >> 36 36 5 2 >> 37 37 4 1 >> 38 38 3 0 >> 39 39 2 0 >> 40 40 1 0 >> >> >> >> >> >> dat <- within(dat,sampleNo[sample(var1[(var1%%2 == 0) & >> sampleNo==0],10,rep=FALSE)] <- 2) >> >> >> >> >> Bert Gunter >> >> "The trouble with having an open mind is that people keep coming along and >> sticking things into it." >> -- Opus (aka Berkeley Breathed in his "Bloom County" comic strip ) >> >> On Mon, Sep 25, 2017 at 10:27 AM, David Studer <[email protected]> >> wrote: >> >> > Hello everybody! >> > >> > I have the following problem: I'd like to select a sample from a >> subsample >> > in a dataset. Actually, I don't want to select it, but to create a new >> > variable sampleNo that indicates to which sample (one or two) a case >> > belongs to. >> > >> > Lets suppose I have a dataset containing 40 cases: >> > >> > data <- data.frame(var1=seq(1:40), var2=seq(40,1)) >> > >> > The first sample (n=10) I drew like this: >> > >> > data$sampleNo <- 0 >> > idx <- sample(seq(1,nrow(data)), size=10, replace=F) >> > data[idx,]$sampleNo <- 1 >> > >> > Now, (and here my problems start) I'd like to draw a second sample >> (n=10). >> > But this sample should be drawn from the cases that don't belong to the >> > first sample only. *Additionally, "var1" should be an even number.* >> > >> > So sampleNo should be 0 for cases that were not drawn at all, 1 for >> cases >> > that belong to the first sample and 2 for cases belonging to the second >> > sample (= sampleNo equals 0 and var1 is even). >> > >> > I was trying to solve it like this: >> > >> > idx2<-data$var1%%2 & data$sampleNo==0 >> > sample(data[idx2,], size=10, replace=F) >> > >> > But how can I set sampleNo to 2? >> > >> > >> > Thank you very much for your help! >> > >> > David >> > >> > [[alternative HTML version deleted]] >> > >> > ______________________________________________ >> > [email protected] 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]] >> >> ______________________________________________ >> [email protected] 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/posti >> ng-guide.html >> and provide commented, minimal, self-contained, reproducible code. >> > > [[alternative HTML version deleted]] ______________________________________________ [email protected] 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.
