So does each person have multiple rows and you want to sample the set of rows?
The usual approach that I take is to split them into a list, sample from the list, the put the list back together, for example: tmp1 <- split(as.data.frame(state.x77), state.division) tmp2 <- sample(tmp1, replace=TRUE) tmp3 <- do.call( 'rbind', tmp2 ) tmp3$newid <- rep( 1:length(tmp2), sapply(tmp2, nrow) ) wrap that in a function and you have the bootstrap resampling. Hope this helps, -- Gregory (Greg) L. Snow Ph.D. Statistical Data Center Intermountain Healthcare greg.s...@imail.org 801.408.8111 > -----Original Message----- > From: r-help-boun...@r-project.org [mailto:r-help-boun...@r- > project.org] On Behalf Of Chris__ Barker > Sent: Thursday, April 29, 2010 5:26 PM > To: r-help@r-project.org > Subject: [R] understanding behavior of "merge" > > I'm trying to bootstrap resample from a repeated measures dataset. I > sample > a vector of "ID"'s from my dataframe with replacement. > Then I merge this back with my dataframe. > I'm re-sampling subjects in the dataset rather than rows of the data. > > I thought I could use the left/right join features of the merge to > select > the records I want from the dataframe (mydataframe), like this. > > boot.sample <- merge( id.boot.draw,mydataframe, by=c("ID") , > all.x=TRUE ) > > > when I do that, the correct records are selected from "mydataframe" but > the > values for all the variables, other than the matching variable are now > "NA". > > My other option is to right a for loop, which I would hope to avoid. > > Thanks in advance for any suggestions > > -- > Chris Barker, > > [[alternative HTML version deleted]] > > ______________________________________________ > 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.