[R] lattice: horizontal alignment of labels in key

[Paul Murrell]

Hi


Thomas Zumbrunn wrote:
> Dear R users
> 
> I have problems horizontally aligning labels in keys of lattice plots when the 
> labels make use of plotmath. Here's a self-contained example:
> 
> dat <- data.frame(x = rnorm(10),
>                   y = rnorm(10),
>                   z = factor(rep(c("a", "b"), each = 5)))
> xyplot(y ~ x, dat, groups = z,
>        auto.key = list(columns = 2,
>          text = c(expression(plain("alright")),
>            expression(italic("too low")))))
> 
> It seems like the grid object which the lattice function creates from the key 
> arguments has different heights for the two labels since the second label does 
> not stretch over the baseline.


I think the basic problem here is that mathematical expressions work 
with the limits of bounding boxes rather than an overall baseline.  A 
workaround is to use phantom() within the expression to introduce 
elements with a consistent height that are not actually drawn.  For 
example ...

xyplot(y ~ x, dat, groups = z,
        auto.key = list(columns = 2,
          text = c(expression(plain("alright")*phantom("hg")),
            expression(italic("too low")*phantom("hg")))))

... which forces both expressions to go as high as the top of an "h" and 
as low as the bottom of a "g" without those characters being drawn 
(although space is allowed for those characters so you get a bit of 
blank horizontal space).

Paul


> Any ideas how I could circumvent the problem (other than manipulating the key 
> grob)?
> 
> Best wishes
> Thomas Zumbrunn
> 
> ______________________________________________
> 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.

-- 
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/