[R] plot POSIXct format data

[Prof Brian Ripley]

On Tue, 15 Jan 2008, Jingru Dai wrote:

> Hi, everyone
>
> I've been trying to make a scatter plot of POSIXct format data to see
> the difference between two start time.
> Like X:
> [1] "1995-05-26 19:00:00" "1995-05-27 01:00:00" "1995-05-27 07:00:00"
> [4] "1995-06-29 01:00:00" "1995-06-29 07:00:00" "1995-06-30 13:00:00"
> [7] "1995-06-30 19:00:00" "1995-07-01 01:00:00" "1995-07-01 07:00:00"
> ......
> Y:
> [1] "1995-05-26 19:00:00" "1995-05-27 01:00:00" "1995-05-27 07:00:00"
> [4] "1995-06-29 01:00:00" "1995-06-29 07:00:00" "1995-06-30 13:00:00"
> [7] "1995-06-30 19:00:00" "1995-07-01 01:00:00" "1995-07-01 07:00:00"
> .......
>
> But it seems plot(x,y) doesn't work, y have to be numeric format.  Is
> there any special command for that or I should change the format of the
> data?

It's possible, but there is not a canned solution.  You could look at the 
code of graphics:::plot.POSIXct and modify to treat x the same way as y. 
Or simply use

plot(x,y, xaxt="n", yaxt="n")
axis.POSIXct(1, x)
axis.POSIXct(2, y)


> Thanks
>
> Jingru Dai
> ----
> School of Mathematical Sciences
> Rm 454, Building 28
> Monash University, 3800
> Victoria, Australia

-- 
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