[R] POSIXct dates on x-axis using xyplot

[Deepayan Sarkar]

On 9/10/07, jim holtman <jholtman at gmail.com> wrote:
> I am using 'xyplot' in lattice to plot some data where the x-axis is a
> POSIXct date.  I have data which spans a 6 month period, but when I
> plot it, only the last month is printed on the right hand side of the
> axis.  I would have expected that at least I would have a beginning
> and an ending point so that I have a point of reference as to the time
> that the data spans.  Here is some test data.
>
>
> > # create test data
> > dates <- seq(as.POSIXct('2006-01-03'), as.POSIXct('2006-06-26'), by='1 week')
> > my.data <- seq(1, length=length(dates))
> > require(lattice)
> [1] TRUE
> > # plot only shows a single month ("Jul" on the right).  Would have
> > # expected at least the beginning and the ending month since this spans
> > # a 6 month period
> > pdf('/test.pdf')
> > xyplot(my.data ~ dates)
> > dev.off()

Yes, the calculations seem very sensitive to the exact range (probably
because you are close to the beginning of a year); e.g., the first two
seem fine, but things are not nice for anything bigger.

xyplot(my.data ~ dates, lattice.options = list(axis.padding =
list(numeric = 0)))

xyplot(my.data ~ dates, lattice.options = list(axis.padding =
list(numeric = 0.01)))

xyplot(my.data ~ dates, lattice.options = list(axis.padding =
list(numeric = 0.02)))

Your options are

(1) specify tick locations manually, using scales$x$at -- this should
work, but I haven't checked

(2) provide a patch for lattice:::formattedTicksAndLabels.POSIXct that
gives behaviour that you like

The current version is derived from axis.POSIXct, which, incidentally,
can also be made to do odd things:

dates <- c(as.POSIXct('2005-12-30'), as.POSIXct('2006-07-01'))
my.data <- seq(1, length=length(dates))
plot(dates, my.data)


-Deepayan