Chabot Denis wrote: > Dear R users, > > I need to reorder a dataframe using 3 variables for the determine the > sorting order. > > When I create a simple dataframe to test the method, things work as I > expected: > > a1 <- rep(1:10, each=8) > a2 <- rep(rep(1:2, each=4), 10) > a3 <- rep(c(1:4),20) > (a <- data.frame(a1, a2, a3)) > > for each combination of a1 and a2, a3 is increasing > > t <- order(a$a1, a$a2, rev(a$a3)) > b <- a[t,] > Using "rev(a$a3)" messes things up when the values of a3 aren't identical in every (a1, a2) group. If you know a3 is numeric with no NA or NaN values, you could use
t <- order(a$a1, a$a2, -a$a3) to get the sort order reversed. If not, you need to do two sorts, relying on the fact that order uses a stable sort: t1 <- order(a$a3, decreasing=TRUE) t2 <- with(a[t1,], order(a1, a2)) t <- t1[t2] b <- a[t,] It would be nice if the decreasing arg to order was allowed to be a vector, with entries applied in the obvious way, so that t <- with(a, order(a1, a2, a3, decreasing = c(FALSE, FALSE, TRUE))) would work, but alas, it doesn't. Duncan Murdoch > In this new dataframe, the 3rd variable is in decreasing order within > each combination of a1 and a2, which is the desired result. > As expected, this still works if the second variable never changes: > > e1 <- rep(1:10, each=8) > e2 <- rep(2, 80) > e3 <- rep(c(1:8),10) > e <- data.frame(e1, e2, e3) > t <- order(e$e1, e$e2, rev(e$e3)) > f <- e[t,] > > With my real data, I do not get the 3rd variable in inverse order for > each combination of the first 2. Here I recreate the beginning of my > dataframe for you to see what I mean: > > c1 <- c(rep(813,102), rep(826,48)) > c2 <- rep(2,150) > c3 <- c(seq(1:102), seq(1,48)) > c <- data.frame(c1, c2, c3) > t <- order(c$c1, c$c2, rev(c$c3)) > d <- c[t,] > > The dataframe d is properly ordered for c1==826, but not for c1==813, > where c3 goes from 48 down to 1, and then from 102 down to 49, > instead of going from 102 down to 1. All the variables are numeric, > not factors. > > Any help/explanation will be greatly appreciated. > > Denis > sessionInfo() > R version 2.6.0 (2007-10-03) > powerpc-apple-darwin8.10.1 > > locale: > fr_CA.UTF-8/fr_CA.UTF-8/fr_CA.UTF-8/C/fr_CA.UTF-8/fr_CA.UTF-8 > > attached base packages: > [1] stats graphics grDevices utils datasets methods base > > ______________________________________________ > 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.
