[R] lattice xyplot - aligning date labels so that they align with the grid lines in panel.grid

[Deepayan Sarkar]

On 6/19/06, john.gavin at ubs.com <john.gavin at ubs.com> wrote:
> Hi,
>
> I have a basic question about aligning date labels for the x-axis
> in an xyplot so that they align with the grid lines
> from the panel.grid argument.
>
> For example, with
>
> x <- data.frame(
>   date = seq(as.Date("2005/01/01"), as.Date("2006/06/01"),
>   length.out = 20), value = runif(20))
> xyplot(value ~ date, data = x,
>   panel = function(x, y, subscripts, ...)
>   { panel.grid(h = -1, v = -1, col = "grey", lwd = 1, lty = 1)
>     panel.xyplot(x, y, ...)
>   })
>
> How can I get the labels on the x-axis to align
> with the vertical grid lines?
> i.e. I have 6 vertical grid lines by default (v = -1)
> in this example so I would like 6 labels along the x-axis
> at the same points, whereas I see only 2 (2005 and 2006).

You will need to do it manually, e.g.:

xyplot(value ~ date, data = x,
       panel = function(x, y, subscripts, ...) {
           panel.grid(h = -1, v = 0, col = "grey", lwd = 1, lty = 1)
           panel.abline(v = as.Date(c("2005/01/01", "2006/01/01")),
                        col = "grey", lwd = 1, lty = 1)
           panel.xyplot(x, y, ...)
       })

For more, you can put in more locations in panel.abline, and the same
locations as tick mark positions in scales$y$at.

> As an alternative I would be happy to just specify the number of labels
> as long as panel.grid's vertical lines aligned with the labels.

Not possible currently, unlikely to be possible ever.

> > R.version.string
> [1] "Version 2.3.1 (2006-06-01)"
>
> on Windows NT4.
>
> Regards,
>
> John.
>
> John Gavin <john.gavin at ubs.com>,
> Commodities, FIRC,
> UBS Investment Bank, 2nd floor,
> 100 Liverpool St., London EC2M 2RH, UK.
> Phone +44 (0) 207 567 4289
> This communication is issued by UBS AG or an affiliate ("UBS...{{dropped}}
>
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-- 
http://www.stat.wisc.edu/~deepayan/