[R] controlling panel.width and panel.height in viewports

[mike townsley]

Dear all,

I'm trying to get a series of lattice levelplots to appear in 
viewports in a particular way but struggling to exert fine control 
over their appearence.  There are two conditions: (a) I only want the 
levelplot to appear (I don't want axes, colour key, etc) in the 
viewport and (b) I want the levelplot to expand to the maximum 
allowable space in the viewport while observing the aspect ratio of the plot.

Condition (a) is OK, but (b) is giving me trouble.  A toy example is:

library(lattice)
library(grid)

x <- 1:10
y <- 1:10
grid <- expand.grid(x=x, y=y)
grid$z <- grid$x*grid$y

asp.ratio.1 <- 2
asp.ratio.2 <- .5
asp.ratio.3 <- 1

test.1 <- levelplot(z~x*y, grid, cuts = 5, xlab="", axes = FALSE,
                     aspect = asp.ratio.1, ylab="", main='', sub="",
                     colorkey = FALSE, region = TRUE, scales = 
list(draw = FALSE))
test.2 <- levelplot(z~x*y, grid, cuts = 5, xlab="", axes = FALSE,
                     aspect = asp.ratio.2, ylab="", main='', sub="",
                     colorkey = FALSE, region = TRUE, scales = 
list(draw = FALSE))
test.3 <- levelplot(z~x*y, grid, cuts = 5, xlab="", axes = FALSE,
                     aspect = asp.ratio.3, ylab="", main='', sub="",
                     colorkey = FALSE, region = TRUE, scales = 
list(draw = FALSE))

# so the three basic types of plot I will have


toy.vp <- viewport(width = .8, height = .8, just = 'centre',
                        name = 'toy')  # this is for my levelplot

X11()
pushViewport(toy.vp)
grid.rect(gp = gpar(col = 'grey'))
print(test.1, newpage = FALSE)

X11()
pushViewport(toy.vp)
grid.rect(gp = gpar(col = 'grey'))
print(test.2, newpage = FALSE)

X11()
pushViewport(toy.vp)
grid.rect(gp = gpar(col = 'grey'))
print(test.3, newpage = FALSE)


I want to get rid of the space (margins) around the longest axis for 
each variety of levelplot.  So I tried to capture the viewport height 
and width and print the levelplot within a region which reflects the 
aspect ratio of the plot.  I run into an error message as below:

width.vp <- convertWidth(grobWidth(grid.rect()), 'cm')
height.vp <- convertWidth(grobHeight(grid.rect()), 'cm')

width.vp;height.vp # this works

if(asp.ratio.1 < 1) {height.vp <- 
unit(as.numeric(height.vp)*asp.ratio.1, "cm")}
if(asp.ratio.1 > 1) {width.vp <- unit(as.numeric(width.vp)/asp.ratio.1, "cm")}

width.vp;height.vp # this also work (ie returns expected results)

print(test.1, panel.width = list(width.vp), panel.height=list(height.vp))

the above command returns this error message:

Error in Ops.unit(panel.height[[1]], panel.width[[1]]) :
         Operator '/' not meaningful for units

What have I missed?

Thanks in advance,

MT

------------------------------------------------------------
Dr Michael Townsley
Senior Research Fellow
Jill Dando Institute of Crime Science
University College London
Second Floor, Brook House
London, WC1E 7HN

Phone: 020 7679 0820
Fax: 020 7679 0828
Email: m.townsley at ucl.ac.uk