Here is a one liner: (yy <- do.call( rbind, sample( split(xx, xx$a) ) ))
Basically reading from inside out, it splits the data frame by a (keeping the structure of b intact within each data frame) and returns it as a list, then that list is randomized, then put back together into a single data frame again. Does this do what you want? -- Gregory (Greg) L. Snow Ph.D. Statistical Data Center Intermountain Healthcare greg.s...@imail.org 801.408.8111 > -----Original Message----- > From: r-help-boun...@r-project.org [mailto:r-help-boun...@r- > project.org] On Behalf Of Tal Galili > Sent: Thursday, August 20, 2009 9:22 AM > To: r-help@r-project.org > Subject: [R] simple randomization question: How to perform "sample" in > chunks > > Hello dear R-help group. > > My task looks simple, but I can't seem to find a "smart" (e.g: non > loop) > solution to it. > > Task: I wish to randomize a data.frame by one column, while keeping the > inner-order in the second column as is. > > So for example, let's say I have the following data.frame: > > xx <-data.frame(a= c(1,2,2,3,3,3,4,4,4,4) , > b = c(1,1,2,1,2,3,1,2,3,4) ) > > I would like to shuffle it by column "a", while keeping the order in > column > "b". > > Here is my "not-smart" way of doing it: > > # R example > xx <-data.frame(a= c(1,2,2,3,3,3,4,4,4,4) , > b = c(1,1,2,1,2,3,1,2,3,4) ) > > randomize.by.column.a <- function(xx) > { > new.a.order <- sample(unique(xx$a)) > new.xx <- NULL > for(i in new.a.order) > { > xx.subset <- xx[ xx$a %in% i ,] > new.xx <- rbind(new.xx , xx.subset) > } > > return(new.xx) > } > randomize.by.column.a(xx) > # END of - R example > > > > I would love for a better, faster, way of doing it. > > Thanks, > Tal > > > > > > > > > > > -- > ---------------------------------------------- > > > My contact information: > Tal Galili > Phone number: 972-50-3373767 > FaceBook: Tal Galili > My Blogs: > http://www.r-statistics.com/ > http://www.talgalili.com > http://www.biostatistics.co.il > > [[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.
