On Thu, May 26, 2011 at 4:34 AM, Paul Murrell <p.murrell at auckland.ac.nz> wrote:
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.
The (newish) pretty.POSIXt method makes this relatively painless:
foo <- as.POSIXct(Sys.Date() + c(0, 365, -365))
grid.newpage()
pushViewport(
plotViewport(
c(5, 5, 4, 2),
xscale = as.numeric(range(foo)),
yscale = c(0,30)
)
)
grid.rect()
p <- pretty(foo)
grid.xaxis(at = p, label = attr(p, "labels"))
p <- pretty(foo, n = 2)
grid.xaxis(at = p, label = attr(p, "labels"), main = FALSE)
-Deepayan
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]]
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-- 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/
______________________________________________ R-help at r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.