Greek Letters for stat density 2d plot

Question

Consider the following plot:

# fake data
set.seed(1234)
n <- 200
gg <- data.frame(wf=rnorm(n,0.5),wb=rnorm(n,0.5),z=runif(n,0,6))

# plot it
gg$`My Title` <- gg$z
ggplot(data=gg, aes(x=wf, y=wb, color=`My Title`)) + 
  geom_point(aes(colour=z),shape="") +
  stat_density2d(aes(fill = ..level..),n = 100,contour = TRUE,geom = "polygon") +
  labs(x=expression(w[f]),y=expression(w[b])) +
  guides(fill=F)

I would like to change My Title to a greek letter or a mixture of text with greek letter. Thanks!

Answer 1

Adding guides(colour=guide_colorbar(title=expression(paste("This is a greek letter: ", alpha)))) should work:

# fake data
set.seed(1234)
n <- 200
gg <- data.frame(wf=rnorm(n,0.5),wb=rnorm(n,0.5),z=runif(n,0,6))

ggplot(data=gg, aes(x=wf, y=wb, color=z)) + 
 geom_point(aes(colour=z),shape="") +
 stat_density2d(aes(fill = ..level..),n = 100,contour = TRUE,geom = "polygon") +
 labs(x=expression(w[f]),y=expression(w[b])) + guides(fill=F) +     
 guides(colour=guide_colorbar(title=expression(paste("This is a greek letter: ", alpha))))