I have the following code ####################################################################
library(zoo) miedate <- yearmon((2006)+seq(0,23)/12) tab <- zoo(cbind(A = c(79.47, 89.13, 84.86, 75.68, 72.82, 78.87, 93.46, 78.18, 82.46, 77.25, 80.95, 84.39, 81.7, 74.76, 65.29, 60.3, 66.59, 73.19, 92.39, 65.76, 77.45, 74.22, 101.36, 100.01), B = c(77.95, 76.73, 51.2, 51.86, 51.29, 49.45, 53.88, 47.96, 55.07, 45.34, 37.07, 37.53, 47.79, 37.5, 30.35, 37.78, 34.13, 39.14, 39.89, 35.46, 36.54, 38.39, 47.33, 45.34)),miedate) par(mai=c(0.75, 0.75, 0.1, 0.1)) my.panel <- function(...) { fmt <- "%b-%Y" # format for axis labels lines(...) panel.number <- parent.frame()$panel.number # if bottom panel if (!length(panel.number) || panel.number == NCOL(tab)) { # next line only if non-labelled ticks wanted for each point axis(1, at = time(tab), lab = FALSE) ix <- seq(1, length(tab), 3) labs <- format(time(tab), fmt) axis(1, at = time(tab)[ix], lab = labs[ix], tcl = -0.7, cex.axis = 0.9) } } plot.zoo(tab, plot.type="single", panel=my.panel, lty=c(1,2,3,4,5,1), lwd=c(8,2,2,2,2,8), col=c("darkorange", "red2","darkblue","darkblue","green","midnightblue"), xlab=" ",ylab = "euro/MWh",xaxt="n") #################################################################### This code produces a graph with a non-decimal x-axis but by far more (human) readable because ticks corresponds to months exactly (and not to a weird decimal ticking!). I would like to add a vertical grid with the same criterium. How can I obtain this? Ciao Vittorio ______________________________________________ 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.