The third phase is determined since there are only three groups, but I should have added them to group specifications to make things clearer:
> require(e1071) > groups <- apply(permutations(3), 1, function(x) paste(x, collapse="/")) > assign <- sample(rep(groups, 10)) > table(assign) assign 1/2/3 1/3/2 2/1/3 2/3/1 3/1/2 3/2/1 10 10 10 10 10 10 ------- David > -----Original Message----- > From: r-help-boun...@r-project.org [mailto:r-help-bounces@r- > project.org] On Behalf Of David L Carlson > Sent: Wednesday, August 22, 2012 5:11 PM > To: 'Daniel Nordlund'; r-help@r-project.org > Subject: Re: [R] Iterative sampling with restrictions > > If I understand you, this is just random assignment over 6 groups: 1/2, > 1/3, > 2/1, 2/3, 3/1, 3/2. > > > groups <- c("1/2", "1/3", "2/1", "2/3", "3/1", "3/2") > > assign <- sample(rep(groups, 10)) > > table(assign) > assign > 1/2 1/3 2/1 2/3 3/1 3/2 > 10 10 10 10 10 10 > > ---------------------------------------------- > David L Carlson > Associate Professor of Anthropology > Texas A&M University > College Station, TX 77843-4352 > > > -----Original Message----- > > From: r-help-boun...@r-project.org [mailto:r-help-bounces@r- > > project.org] On Behalf Of Daniel Nordlund > > Sent: Tuesday, August 21, 2012 2:58 AM > > To: r-help@r-project.org > > Subject: Re: [R] Iterative sampling with restrictions > > > > > -----Original Message----- > > > From: r-help-boun...@r-project.org [mailto:r-help-bounces@r- > > project.org] > > > On Behalf Of David A. Kim > > > Sent: Monday, August 20, 2012 9:17 PM > > > To: r-help@r-project.org > > > Subject: [R] Iterative sampling with restrictions > > > > > > Hi all, > > > > > > I'm working on a seemingly trivial problem that I can't figure out > > how > > > to implement in R. I'd be most grateful for any help here. > > > > > > I want to do the following: first, randomly assign each of n units > to > > > one of g groups of size n/g. Then, randomly re-assign each of the n > > > units to a different group (i.e., same as the first step, but the > > unit > > > can't be assigned to a group to which it's already belonged). Then > > > repeat this step until each unit has at some point been assigned to > > > every group. > > > > > > More concretely, say I have 60 units and 3 groups into which to > > divide > > > the units. I could first do something like: > > > > > > group1<-sample(1:60,20) > > > group2<-sample(setdiff(1:60,group1),20) > > > group3<-sample(setdiff(1:60,c(group1,group2)),20) > > > > > > But then how to randomly re-assign group membership such that all > > > units are assured a different group assignment in the second "wave" > > of > > > grouping? Just narrowing the sampling pool to those units that > > > weren't previously assigned to a given group won't work (consider > the > > > case where groups 1 and 2 swap units: in the second wave, there > would > > > be no units to assign to group 3 as all the remaining units had > > > already been in group 3 in the first wave). > > > > > > Most grateful for any assistance, > > > > > > David > > > > > > > David, > > > > I would collect the sample waves into a data.frame. I am sure > someone > > will be able to help you with a more general and/or efficient > solution, > > but to get you started I have provided one possible solution to your > 60 > > unit 3 wave example > > > > #create data.frame with IDs > > df <- data.frame(id=1:60) > > > > #create first sample wave > > df$wave1 <- sample(rep(1:3,20)) > > > > #reorder df and create second wave sample > > df <- df[order(df$wave1),] > > df$wave2 <- c(sample(rep(c(2,3),10)), > > sample(rep(c(1,3),10)),sample(rep(c(1,2),10))) > > > > #now use set diff to create 3rd wave > > for(i in 1:60) df[i,'wave3'] <- unlist(setdiff(1:3,df[i,2:3])) > > > > df > > > > > > Hope this is helpful, > > > > Dan > > > > Daniel Nordlund > > Bothell, WA USA > > > > ______________________________________________ > > R-help@r-project.org mailing list > > 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. > > ______________________________________________ > R-help@r-project.org mailing list > 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. ______________________________________________ R-help@r-project.org mailing list 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.
