[R] Problem using plot and converted dates

[Prof Brian Ripley]

On Mon, 17 Apr 2006, s.e.roberts at qmul.ac.uk wrote:

Please do follow the posting guide and at least tell us your version of R 
and give a working example (mkf is missing)

> Dear R-help,
> I am having problems with plotting converted dates in chronological as Mar-03,
> May-03...Jul-04.
> My script is:
>
> sam4<-c("03/03/01","03/05/01","03/07/01","03/09/01","03/11/01","04/01/01","04/03/01","04/05/01","04/07/01")
> sam5<-strptime(sam4,format="%y/%m/%d")

I would suggest you use as.Date here, for you have dates, not date-times.

> f<-data.frame(sam5,mkf)
> plot(f,type="l")
> # This works ok, but none of the labels appear on the x-axis,

It works for me: it is not intended to plot your labels (and plot.default 
does not do that either).  If you want add a special axis, use axis.Date 
to do so.

> so I thought I
> would convert them using
> # as.POSIXct:

You have converted them to a factor, which is not what you want.

> sam6<-format(as.POSIXct(sam5), "%b-%y")
> mon<-factor(as.character(sam6),levels=sam6)
> f2<-data.frame(mon,mkf)
> plot(f2,type="l")
>
> The problem is that plot(f2,type="l") no longer produces a line plot...

Why don't you use plot(sam5, mkf, type="l")?  That works, and in fact
your example works in R 2.3.0RC, but creating a data frame you don't need 
is counter-productive.

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595