levelplot with linear color spacing

levelplot_scale.R

# Make a levelplot with a custum linear scale
# Author: Bryan Urban
# Email: burban at fraunhofer dot org
# Date: 2015-04-30 

library(lattice)
library(RColorBrewer)

# make some data
foo <- foo <- expand.grid(x = 1:100, y=1:10)
foo$z <- rnorm(100*10)*10

# select color palette
my.cols <- rev(brewer.pal(11, "RdYlGn")) 

# pick levels so each gradation contains 10% of the data
# my.at <- quantile(foo$z, seq(0, 1, length.out=21), na.rm=TRUE)
# ncuts <- length(my.at)-1

# - or - 

# pick levels so each gradation is equally spaced
ncuts <- 10 # number of cuts
my.rng <- range(foo$z)
by <- ceiling((ceiling(my.rng[2]) - floor(my.rng)[1])/(ncuts))
my.at <- seq(from = floor(my.rng[1]), 
             to = floor(my.rng[1])+(ncuts+1)*by, 
             by=by)
cols <- colorRampPalette(my.cols)(ncuts+1)

#lp_temp <- 
  levelplot(z~reorder(x, z, mean, na.rm=TRUE)*
              reorder(y, z, mean, na.rm=TRUE),
            foo, # xlim=c(0,10),
            ylab="y", xlab="x",
            cuts= ncuts,
            at=my.at,
            col.regions=cols,
            scales=list(y=list(at=""), # x=list(at=seq(0,10,by=2)),
                        alternating=c(1,0,1,0)),
            colorkey=list(at=my.at,
                          labels=list(at=my.at)
                          #space="left"
                          )
  )