Change legend title position with no change in labels

Question

I am building off a question asked earlier, geom_tile single color as 0... It starts with the following code and the provided answer code creates the plot:

df <- data.frame(expand.grid(1:10,1:10))
df$z <- sample(0:10, nrow(df), replace=T)
# provided answer from SO
ggplot(df,aes(x = Var1,y = Var2, fill = z)) + 
  geom_tile() + 
  scale_fill_gradientn(colours = c("white", "green", "red"), values = c(0,0.1,1))

I would like to move the legend to the bottom with the legend title on top and centered. The code and result are here:

ggplot(df,aes(x = Var1,y = Var2, fill = z)) + 
  geom_tile() + 
  scale_fill_gradientn(colours = c("white", "green", "red"), values = c(0,0.1,1)) +
  theme(legend.position="bottom") +
  guides(fill = guide_legend(title.position="top",label.position = "bottom"))

Repositioning the legend works and the title is on "top" but I lost the continuous scale and can't center the title. There are a number of informative q&a on SO about changing legend title position but none seem to have the problem of having a continuous legend changed to discreet.

Answer 1

This is how you want it?

ggplot(df,aes(x = Var1,y = Var2, fill = z)) + 
  geom_tile() + 
  theme(legend.position="bottom") +
  scale_fill_gradientn(colours = c("white", "green", "red"),
                       values = c(0, 0.1, 1)) +
  guides(fill = guide_colourbar(title.position = "top",
                                title.hjust = .5,
                                label.position = "bottom"))