On 31/03/2015 1:05 PM, Kevin E. Thorpe wrote: > Hello. > > I am trying to simulate recruitment in a randomized trial. Suppose I > have three streams (strata) of patients represented by these data frames. > > df1 <- data.frame(strat=rep(1,10),id=1:10,pid=1001:1010) > df2 <- data.frame(strat=rep(2,10),id=1:10,pid=2001:2010) > df3 <- data.frame(strat=rep(3,10),id=1:10,pid=3001:3010) > > What I need to do is construct a data frame with all of these combined > where the order of selection from one of the three data frames is > randomized but once a stratum is selected patients are selected > sequentially from that data frame. > > To see what I'm looking to achieve, suppose the first five subjects were > to come, in order, from strata (data frames) 1, 2, 1, 3 and 2. The > expected result should look like this: > > rbind(df1[1,],df2[1,],df1[2,],df3[1,],df2[2,]) > strat id pid > 1 1 1 1001 > 2 2 1 2001 > 21 1 2 1002 > 4 3 1 3001 > 22 2 2 2002 > > I hope what I'm trying to accomplish makes sense. Maybe I'm missing > something obvious, but I really have no idea at the moment how to > achieve this elegantly. Since I need to simulate many trial recruitments > it needs to be general and compact. > > I appreciate any advice.
How about something like this: # Permute an ordered vector of selections: sel <- sample(c(rep(1, nrow(df1)), rep(2, nrow(df2)), rep(3, nrow(df3)))) # Create an empty dataframe to hold the results df <- data.frame(strat=NA, id=NA, pid=NA)[rep(1, length(sel)),] # Put the original dataframes into the appropriate slots: df[sel == 1,] <- df1 df[sel == 2,] <- df2 df[sel == 3,] <- df3 # Clean up the rownames rownames(df) <- NULL Duncan Murdoch ______________________________________________ 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.
