Custom color for scale_size_continuous()-CodePudding

In the plot below, how do I show all cty >= 30 values in color green and cty < 30 values in red? Thanks!

library(ggplot2)
data(mpg)
p <- ggplot()  
    geom_point(data = mpg, aes(displ, manufacturer, size = cty), alpha = 0.2)  
    scale_size_continuous(breaks = c(30, 20, 10))  
    scale_color_manual(values = c("green", "red", "red"))  # does not work
p

CodePudding user response：

I don't think there are any cty values greater than 30 in the dataset, but since it is only an example, let's make the cutoff 15:

ggplot()  
    geom_point(data = mpg, aes(displ, manufacturer, size = cty, 
                               color = cty <= 15), alpha = 0.2)  
    scale_size_continuous(breaks = c(30, 20, 10))  
    scale_color_manual(values = c("green", "red"))

If you want the legends merged, you would need a continuous color scale that emulated a discrete one, so something like:

ggplot()  
    geom_point(data = mpg, aes(displ, manufacturer, size = cty, 
                               color = cty), alpha = 0.2)  
    scale_size_continuous(breaks = c(30, 20, 10))  
    scale_color_gradientn(colors = c("red", 'red', "green", 'green'),
                          values = c(0, 0.5, 0.50001, 1),
                          breaks = c(30, 20, 10),
                         guide = guide_legend())