scale caption on levelplot

hi,

i am trying to figure out how to put a caption on the colour scale  
of a
levelplot. there does not seem to be an option for this in  
levelplot().

Agreed. I could not find one in the levelplot help page or in the  
chapter of Lattice on legends and keys. Sarkar basically says you need  
to use grid calls if you want to go beyond the basics.

i tried using mtext() but as soon as you put the text far out enough  
on
the right of the plot, it goes beyond the plot boundary. so i tried to
extend the margin on the right of the plot using par(mar) but this did
not have any effect on the plot area.

i would really appreciate some help with this because having a caption
on a colour scale is rather fundamental and certainly something that a
journal referee is going to pick up on!

Your question has no reproducible example but suggests that you do not  
understand that levelplot is a lattice function and that lattice uses  
grid graphics. The par arguments that lattice understands (or is  
willing to deal with gracefully) are passed through trellis.par.set().  
The current settings are accessible with:

trellis.par.get()

  Since lattice is implemented with grid graphics, you may get useful  
information from:

require(grid)   # lattice apparently loads gpar and its help page but  
doesn't
                 # actually load grid. (I don't understand this. )
?gpar()   # Which has examples that may allow you to get a better  
understanding
           # of how to layer new material on top of existing grid  
graphics.

David Winsemius, MD
West Hartford, CT

Andrew,
see below

On Dec 4, 2010, at 8:25 AM, Andrew Collier wrote:

hi,

i am trying to figure out how to put a caption on the colour scale
of a
levelplot. there does not seem to be an option for this in
levelplot().

Agreed. I could not find one in the levelplot help page or in the
chapter of Lattice on legends and keys. Sarkar basically says you need
to use grid calls if you want to go beyond the basics.

i tried using mtext() but as soon as you put the text far out enough
on
the right of the plot, it goes beyond the plot boundary. so i tried to
extend the margin on the right of the plot using par(mar) but this did
not have any effect on the plot area.

i would really appreciate some help with this because having a caption
on a colour scale is rather fundamental and certainly something that a
journal referee is going to pick up on!

Your question has no reproducible example but suggests that you do not
understand that levelplot is a lattice function and that lattice uses
grid graphics. The par arguments that lattice understands (or is
willing to deal with gracefully) are passed through trellis.par.set().
The current settings are accessible with:

trellis.par.get()

   Since lattice is implemented with grid graphics, you may get useful
information from:

require(grid)   # lattice apparently loads gpar and its help page but
doesn't
                  # actually load grid. (I don't understand this. )
?gpar()   # Which has examples that may allow you to get a better
understanding
            # of how to layer new material on top of existing grid
graphics.

As David says, you need to use trellis parameters, in this case
presumably trellis.par.get('layout.widths') and
trellis.par.get('layout.heights') will be useful. You can add
appropriate settings to your levelplot() call with the
par.settings argument. After you adjust the amount of space
you want, you can then use grid::grid.text() to add your text.
Here's an example:

   library(grid)
   x <- sort(rnorm(100,50,10))
   y <- sort(runif(100,0,20))
   d <- expand.grid(x=x, y=y)
   d$z <- x + y
   graphics.off()
   p <- levelplot(z ~ x*y, d,
             par.settings=list(
               layout.widths=list(right.padding=4),
               layout.heights=list(top.padding=6)),
             colorkey = TRUE)
   print(p)

   ## now add the text
   grid.text('here and there', x=.98, y=.5, rot=-90,
     gp = gpar(col=4,
         fontfamily="HersheyGothicEnglish", cex=2))
   grid.text('here\nand\nthere', x=.88, y=.92,
     gp = gpar(lineheight=.75, col=3))

Peter Ehlers

hi peter and david,

thanks for the excellent suggestions. here is something like what i am
finally using (those fancy fonts were really tempting, but i chose
something a little more mundane!):

library(lattice)

x <- sort(rnorm(100,50,10))
y <- sort(runif(100,0,20))
d <- expand.grid(x=x, y=y)
d$z <- x + y
plot.new()
p = levelplot(z ~ x*y, d,
               par.settings=list(
                 layout.widths=list(right.padding=4)),
               colorkey = TRUE)
print(p)

mtext("CAPTION", 4, 1)

your help really appreciated!

best regards,
andrew.

Andrew B. Collier

Physicist
Waves and Space Plasmas Group
Hermanus Magnetic Observatory

Honorary Senior Lecturer                             tel: +27 31 2601157
Space Physics Research Institute                     fax: +27 31 2607795
University of KwaZulu-Natal, Durban, South Africa    gsm: +27 83 3813655

hi peter and david,

thanks for the excellent suggestions. here is something like what i am
finally using (those fancy fonts were really tempting, but i chose
something a little more mundane!):

library(lattice)

x<- sort(rnorm(100,50,10))
y<- sort(runif(100,0,20))
d<- expand.grid(x=x, y=y)
d$z<- x + y
plot.new()
p = levelplot(z ~ x*y, d,
                par.settings=list(
                  layout.widths=list(right.padding=4)),
                colorkey = TRUE)
print(p)

mtext("CAPTION", 4, 1)

Even if that worked (it doesn't for me), you're still mixing
base (or tradtional) graphics with lattice graphics. Not a
good idea. I would replace the plot.new call with

  trellis.device()

and then, after the levelplot, replace the mtext with
grid.text(...) as I suggested originally. You'll have
to fiddle a bit with the x location but that should
be easy to get the way you want.

One more thing, since you imply that this is for
publication, it's a good idea to create the plot close
to the size that will ultimately be printed; resizing
is always better avoided.

Peter Ehlers

your help really appreciated!

best regards,
andrew.