How can I force ggplot's geom_tile to fill every facet?

Question

I am using ggplot\'s geom_tile to do 2-D density plots faceted by a factor. Every facet\'s scale goes from the minimum of all the data to the maximum of all the data, but th

Answer 1

I think you're looking for a combination of scales = "free" and expand = c(0,0):

ggplot(mydata) +
  aes(x=x,y=y) +
  stat_density2d(geom="tile", aes(fill = ..density..), contour = FALSE) +
  facet_wrap(~ groupvar,scales = "free") + 
  scale_x_continuous(expand = c(0,0)) + 
  scale_y_continuous(expand = c(0,0))

EDIT

Given the OP's clarification, here's one option via simply setting the panel background manually:

ggplot(mydata) +
  aes(x=x,y=y) +
  stat_density2d(geom="tile", aes(fill = ..density..), contour = FALSE) +
  facet_wrap(~ groupvar) + 
  scale_fill_gradient(low = "blue", high = "red") + 
  opts(panel.background = theme_rect(fill = "blue"),panel.grid.major = theme_blank(),
       panel.grid.minor = theme_blank())