[R] Three questions about plotting

[David Parkhurst]

I would like to plot three graphs, one above the other, of three “y” 
variables that have different scales against a common Date variable, as 
with the code below.

Q1.  If I understand correctly, I can't use lattice graphics because my 
y's have different scales.  Is that correct?  All the lattice or trellis 
plots I've seen have common “y” scales for all plots.

I have two problems with what this code produces:
Q2.  How can I get the vertical dimension of all three plots to be the 
same?  I know that I've made them different by using different mar 
numbers, but I had to do that, I thought, to leave room for date axis 
labels.  I don't want to leave wasted space between the plots.

Q3.  Why are my dates not coming out in the format I've specified in the 
axis.Date statement?

DateNum <- seq(8248,9247)
Date<-as.Date(DateNum, origin="1970/01/01")
y1<- runif(1000,0,1)
y2<- runif(1000,0,100)
y3<- runif(1000,0,10)
par(mfrow=c(4,1))
par(mar=c(0,4,0,2)+0.1)
plot(y1 ~ Date, xaxt = "n", type = "p",cex=0.7)
plot(y2 ~ Date, xaxt = "n", type = "p",cex=0.7)
par(mar=c(4,4,0,2)+0.1)
plot(y3 ~ Date, xaxt = "n", type = "p",cex=0.7)
DateLbls <- 
seq.Date(from=as.Date("1992/08/01"),to=as.Date("1995/04/27"),by="3 months")
axis.Date(side=1,Date,at=DateLbls, labels=DateLbls, format="%m-%y")