Using dates on axis with Grid plots

Hi

On 15/05/2011 2:01 a.m., Larry White wrote:

Hi,

I'm trying to use Grid plots and would like to have an X axis that
represents dates. I have several years of data so I would like to be able
to
have labeled tick marks only intermittently (not one per date). ?I can
transform the initial data from a date time string into POSIXlt or
POSIXct,
or Date objects.

The issue is that when I try to layout the plot using:

dev.off()
? pushViewport(
? ? plotViewport(
? ? ? c(5, 5, 4, 2),
? ? ? ? xscale=c(
? ? ? ? ? ?min(foo),
? ? ? ? ? ?max(foo)),
? ? ? ? ? ?yscale=c(0,30)
? ? )
)

I get this error, regardless of whether "foo" is formated as POSIXlt,
POSIXct or Date for the xscale.

Error in valid.viewport(x, y, width, height, just, gp, clip, xscale,
yscale,
?:
? Invalid 'xscale' in viewport

How does one specify the scale? ?In the end, I would prefer something like
"2007 ? 2008", etc. to appear on the axis and, of course, I'd actually
want
to plot the data with an x axis of dates. I'm not yet far enough to see if
that's going to be an issue.

The viewport scale has to be numeric. ?Dates are not supported at all by
grid.xaxis() or grid.yaxis(). ?If your dates are just days, you can
as.numeric() them to get a useful range and then pretty() and
as.Date(origin="1970-01-01") to get useful labels for tick marks, but the
general solution is more complex (see axis.Date()). ?Depending on what your
plots need to look like, another approach would be to customize a 'lattice'
plot because it provides support for date-based ?axes.

Paul

Apologies if this is a stupid question, but it's very hard to search for
Grid examples on the web, because "grid" is a very common term in R
plotting
generally.

? ? ? ?[[alternative HTML version deleted]]

--
Dr Paul Murrell
Department of Statistics
The University of Auckland
Private Bag 92019
Auckland
New Zealand
64 9 3737599 x85392
paul at stat.auckland.ac.nz
http://www.stat.auckland.ac.nz/~paul/