[R] Troubles with the format of dates

[Kathi]

Dear useRs,

I'm struggling again with date-related stuff: I am using R to draw water levels at certain measuring 
stations. My data comes as a tab-delimited text file and looks like this:

DATUM	P1	P2
...
2006-11-16	    425.21	423.99		
2006-12-15     425.12	423.97		
2007-01-16	    425.16	424.06	
...

(measurements started in July 2004 and still continue on a monthly or bi-weekly basis)

This is then plotted using this code:

a<-read.table("dummy_data.tab", sep="\t", header=TRUE, na.strings=c(0))
x<-as.Date(a$DATUM)

plot(x, a$P1, axes=FALSE, xlim=c(as.Date("2004-07-01"), as.Date("2009-01-01")), 
ylim=c(423,428), col="red", pch=15, type="o", ylab="Kote [m a.s.l.]", 
main="Dummy Plot")
points(x, a$P2, col="red", pch=17, type="o", lty="dotted")
axis(2, at=423:428, tck=1, col="gray60")
axis.Date(1, at=seq(as.Date("2004-07-01"), as.Date("2009-01-01"), 
by="month"), labels=seq(as.Date("2004-07-01"), as.Date("2009-01-01"), 
by="month"), tck=1, col="gray60")

So far, I've been using this type of date format (yyyy-mm-dd) because that was the only way I could 
get  the whole thing to work when I started using R. However, living in Switzerland, I would prefer 
the dates to read 16.11.2006 i.e. dd.mm.yyyy or 16. Nov. 2006 (preferably using German names for 
the months, if possible). 

I've used the chron package to convert my dates to day mon year (16 Nov 2006, with or without 
spaces), i.e. I replaced the second line of code with:

x<-format(chron(as.character(a$DATUM), format="y-m-d", out.format="day mon year"))

but then I can't plot them any more, because as.Date() no longer is the correct function and R gives 
me an error saying there is an invalid xlim-value. Can someone please point me in the right 
direction?

I could easily change the input data to be in dd.mm.yyyy format, if that helps.

Thanks for your help,

Kathi


--
DropNet AG - Das Unternehmen fuer Ihren Internet-Auftritt!