[R] Controlling graphics parameters in lattice

[Deepayan Sarkar]

On Friday 06 December 2002 10:37 am, Michael Friendly wrote:
> I'm just starting to work with lattice graphics, and am
> having difficulty understanding how to control various graphic
> parameters (font sizes, etc.).  [I'm actually using xyplot
> via plot.effect() in the car package, and would like to be
> able to set some global defaults.]
>
> I read ?xyplot and ?trellis.par.set-- which contains no complete
> list of parameters, just a reference to print(trellis.par.get())
>
> > print(trellis.par.get())
>
> $fontsize
> $fontsize$default
> [1] 10

I get a much longer list.

> I tried
>
> > trellis.par.set("fontsize", 12)
> >  data(quakes)
> >      Depth <- equal.count(quakes$depth, number=8, overlap=.1)
> >      xyplot(lat ~ long | Depth, data = quakes)
> And this crashes the Rgui (Windows, R 1.6.1).  Is this a buglet
> or did I do something wrong?

You are doing this wrong. ?trellis.par.set gives an example of usage:


     `trellis.par.get' is usually used inside trellis functions to get
     graphical parameters before plotting. Modifications by users via
     `trellis.par.set' is typically done as follows:


     `add.line <- trellis.par.get("add.line")'

     `add.line$col <- "red"'

     `add.line <- trellis.par.set("add.line", add.line)'

(the assignment in the last line is redundant, sorry about that)

Your example, adapted to look like this, would have been:


fsize <- trellis.par.get("fontsize")
fsize$default <- 12
trellis.par.set("fontsize", fsize)

The point you are missing is the value argument to trellis.par.set should be a 
list, even when it has only one component. (I will change trellis.par.set to 
complain when value is not a list.)

A slightly easier way to do this is use

lset(list(fontsize = list(default = 12)))

(This becomes useful when the parameter you are changing has many components,  
but you are changing only one or two.)


> I then tried
>
> >      xyplot(lat ~ long | Depth, data = quakes, scales=list(cex=1.5))
>
> which makes the tick labels larger, but not the axis labels.

That goes into xlab / ylab.

> As well, I'm confused about why the following has no effect
>
> on the background (from a fresh start):
> > library(lattice)
> > trellis.par.set("background", "white")

Same reason. Should be 

trellis.par.set("background", list(col = "white"))

or

lset(list(background = list(col = "white"))

> >  data(quakes)
> >      Depth <- equal.count(quakes$depth, number=8, overlap=.1)
> >      xyplot(lat ~ long | Depth, data = quakes)
>
> Only after I've run xyplot once, I can repeat
>
> > trellis.par.set("background", "white")
> >      xyplot(lat ~ long | Depth, data = quakes)

Probably has to do with the fact that 

trellis.par.get("background")$col is now NULL.

Deepayan