[R] contourplot, xyplot, aspect ratio, mfrow

[Deepayan Sarkar]

On Sunday 02 May 2004 03:30, Patrick Giraudoux wrote:
> Hi,
>
> I am gradually moving from the classical R plot functions to the
> library Lattice
>
> I have some questions about contourplot () and its arguments:
>
> 1/ I am working on geographical coordinates which makes necessary
> that the X (longitude) and Y (latitude) units be represented with the
> same distance on screen. This was obtained in the classical R plots
> with plot.default(x,y, asp=1,...)  and then contour(..., add=T). When
> I try aspect=1 with contour plot, I get a square but not at all the
> aspect ratio I wish: 1 unit on X = one unit on Y = the same distance
> on screen. What goes wrong?

Well, aspect works as documented, so nothing goes wrong. The behaviour 
is just different from asp. You could try 

aspect = diff(range(y))/diff(range(x))

and if your x and y are factors, aspect = "xy" should help. Maybe there 
should be a new option (perhaps aspect = "data") that should do this.

> 2/ I would also be capable to project points and symbols on a
> contourplot (the equivalent of points() and symbols() after plot()
> and contour()), but can hardly guess from the help how to manage
> with.

You need to use a custom panel function (see the section on 'panel' 
in ?xyplot). There's no equivalent of symbols, unfortunately, but 
see ?panel.abline and ?lpoints.

> 3/ I would also appreciate to manage the equivalent of
> par(mfrow=c(2,2)) -or any other numbers of screens- and have a
> "Trellis" plot in each of the sub-screens. It seems that contourplot
> does not comply with and ignore the above parameters. Right or wrong?

Right.

> If so, which approach can solve this problem?

See ?print.trellis. (Note that this also allows you to place trellis 
plots inside grid viewports, which maybe overkill for your use, but 
gives you more flexibility.)

Deepayan