R help - Jan 2012 - Can levelplot colorkeys display a logarithmic scale evenly?

I'm using the {lattice} "levelplot" function to make a (more or
less) 2-d
histogram, and for the most part it's working fine with my data.  However, I
can't get the color key to do what I need.  I can give it labels and custom 
cutoffs, but my cutoff lines (and hence my labels) aren't evenly spaced,
instead
they're more-or-less logarithmic, starting at [0,20,50,100...] and
continuing on
up to 5 million.

Levelplot scales the ticks/labels linearly on the color key, leaving most my 
labels scrunched down atop each other at the bottom and only the last few 
(..."500K","1M","2M","5M") really
visible on the rest of the key.  I want each
gap (no matter its numerical range) to occupy one evenly-spaced
"block" on the
color key, so they're all readable by the user.  I want it to display value
on a
logarithmic scale (0,1,10,100,1000,...).  The colorkey only seems to support 
linear scales (0,2,4,6,8,10,...), at least by default, and I don't see any 
options in the help to change that default.

Does levelplot support this?  Or am I destined to draw the colorkey manually 
(very painfully using polygon calls and user coordinates)?  Or are there other 
levelplot-like functions that would facilitate this?  Any help is appreciated,

- Mike

Mike MacFerrin wrote on 01/05/2012 09:28:56 PM:
> I'm using the {lattice} "levelplot" function to make a (more
or less)
2-d 
> histogram, and for the most part it's working fine with my data. 
However, I 
> can't get the color key to do what I need.  I can give it labels and 
custom 
> cutoffs, but my cutoff lines (and hence my labels) aren't evenly 
> spaced, instead 
> they're more-or-less logarithmic, starting at [0,20,50,100...] and 
> continuing on 
> up to 5 million.
> 
> Levelplot scales the ticks/labels linearly on the color key, leaving 
most my 
> labels scrunched down atop each other at the bottom and only the last 
few 
> (..."500K","1M","2M","5M") really
visible on the rest of the key.  Iwant
each 
> gap (no matter its numerical range) to occupy one evenly-spaced 
> "block" on the 
> color key, so they're all readable by the user.  I want it to 
> display value on a 
> logarithmic scale (0,1,10,100,1000,...).  The colorkey only seems to 
support 
> linear scales (0,2,4,6,8,10,...), at least by default, and I don't see 
any 
> options in the help to change that default.
> 
> Does levelplot support this?  Or am I destined to draw the colorkey 
manually 
> (very painfully using polygon calls and user coordinates)?  Or are 
> there other 
> levelplot-like functions that would facilitate this?  Any help is 
appreciated,
> 
> - Mike

Here's one workaround ...

library(lattice)

dat <- expand.grid(x=15*runif(100), y=100*runif(100))
dat$z <- exp(dat$x) + dat$y^2
dat$lz <- log10(dat$z)

levelplot(lz ~ x * y, dat, at=0:7, colorkey=list(labels=paste("10^",
0:7,
sep="")))

Jean
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