The function that is doing the color assignments is level.colors in the lattice package. Looking at the code confirms that the number of colors should be 1 less than the length of the at variable (the documentation implies that it should be 1 more, looks like a documentation bug to me).
It is possible that at one time the author intended to prepend -Inf and append Inf to the at vector so that it did not need to span the entire range of the data, but that was not implemented. I think I would prefer that fix to changing the documentation. The level.colors function uses the cut function to decide on which color to use, by default cut will put a value that matches a cutpoint in the group to the left, so to answer you original question 3.5 goes into the (2.5,3.5] range rather than the (3.5,4.5] group. level.colors does not allow for changing this (hard coded), so if you want the other behaiviour, you either need to rewrite level.colors, or add a very small number to your data to shift 3.5 and the like into the right bin. Hope this helps, -- Gregory (Greg) L. Snow Ph.D. Statistical Data Center Intermountain Healthcare greg.s...@imail.org 801.408.8111 > -----Original Message----- > From: Antje [mailto:niederlein-rs...@yahoo.de] > Sent: Tuesday, May 05, 2009 1:00 AM > To: Greg Snow; r-h...@stat.math.ethz.ch > Subject: Re: [R] levelplot question > > Hi Greg and all the others, > > thanks for your answer. The color-vector has the same length like the > at-vector > but the recycling cannot be the reason, because only values slightly > above my > "threshold" doe not appear blue. > I cannot find a good explanation of which colors are assigned to which > value > ranges. > > I've made little example: > > #-------------------------------------------------------- > mat <- matrix(seq(1,5, length.out = 12), nrow = 3) > mat[1,2] <- 3.5 > > my.at <- seq(0.5,5.5) > my.col.regions <- rainbow(6) > > graph <- levelplot(t(mat[nrow(mat):1, ] ), at = my.at, col.regions = > my.col.regions) > print(graph) > > windows() > plot(1:10) > legend("topleft", legend = as.character(my.col.regions), col = > my.col.regions, > pch = 18) > #-------------------------------------------------------- > > As you can see the green (position 3 in my.col.regions) disappears > completely > in the levelplot (look at the color range at the right side!). > I guess it might also happen in my case... > > I've tested several cases and it looks like the length of the color- > vector > should be one less than the at vector (which would make sense). > > Then, the rule might apply: > > [ at[1],at[2] ] = color[1] > ( at[2],at[3] ] = color[2] > ... > ( at[n-1],at[n] ] = color[n-1] > > > Please correct me if I'm wrong!!! > > Antje ______________________________________________ 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.
