Thank you very much for your detailed explanation and two solutions, Duncan.
Denis Le 07-10-27 à 12:44, Duncan Murdoch a écrit : > 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.
