[R] How to add e.g. lines to a zoo plot?

[Oliver Faulhaber]

Hi all,

a problem I encounter again and again: I plot a zoo object using "plot" 
and then want to add lines or points to this plot.

I usually circumvent this problem by adding artificial coloumns to the 
zoo object before plotting, but I am sure there's a better solution.

To be specific: Assume I did

   x     <- as.Date(c("2002-01-01","2003-01-01","2004-01-01"))
   y.zoo <- zoo(cbind(y1=c(1,2,3),y2=c(3,4,3)),order.by=x)
   plot(y.zoo)

and want to add a straight line like

   lines(x,c(2,2,2),col="blue")

to the first panel. How can I achieve this? Performing the "lines" does 
indeed create a line, but puts it in the middle of nowhere.

Thanks in advance
Oliver

-- 
Oliver Faulhaber · Heckerstr. 2a · D-68723 Schwetzingen
oliverfaulhaber at gmx.de · http://www.oliver-faulhaber.de