sorry but I can't close this thread with a viable solution other than the following one (i.e. by defining an user function to add line);
I understand that the problem is related to the fact that: mean(log(.)) != log(mean(.)) is but for some reason I can't put all that in practice inside the panel.abline(...) I would appreciate if someone can show me how (sorry but at this point I must give up...), thank you all for the help # code start addLine<- function(a=NULL, b=NULL, v = NULL, h = NULL, ..., once=F) { tcL <- trellis.currentLayout() k<-0 for(i in 1:nrow(tcL)) for(j in 1:ncol(tcL)) if (tcL[i,j] > 0) { k<-k+1 trellis.focus("panel", j, i, highlight = FALSE) if (once) panel.abline(a=a[k], b=b[k], v=v[k], h=h[k], ...) else panel.abline(a=a, b=b, v=v, h=h, ...) trellis.unfocus() } } dotplot(date_sampl_time_recs ~ lower_b_i | site, data=teq, scales=list(x=list(log=TRUE)), xscale.components = xscale.components.logpower, layout=c(5,1), panel = function(x,y,...) { panel.grid(h=53, v=-1, lty="dotted", col="gray") panel.dotplot(x,y,...) medians <- median(x) panel.abline(v=medians, col.line="red", lty="dotted") } ) medie<-as.vector(tapply(teq$lower_b_i,teq$site,mean)) addLine(v=log10(medie), once=TRUE, col="blue", lty="dotted") # code end -- View this message in context: http://r.789695.n4.nabble.com/how-to-add-a-vertical-line-for-each-panel-in-a-lattice-dotplot-with-log-scale-tp4632513p4632991.html Sent from the R help mailing list archive at Nabble.com. ______________________________________________ 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.