ggplot geom_point() with colors based on specific, discrete values

Question

I am trying to plot data points with three different colors for three value ranges. For example:

library(ggplot2)
ggplot(mtcars, aes(wt, mpg)) + geom_point(a         


        

Answer 1

You need to cut your values into intervals:

library(ggplot2)
ggplot(mtcars, aes(wt, mpg)) + 
  geom_point(aes(colour = cut(qsec, c(-Inf, 17, 19, Inf))),
             size = 5) +
  scale_color_manual(name = "qsec",
                     values = c("(-Inf,17]" = "black",
                                  "(17,19]" = "yellow",
                                  "(19, Inf]" = "red"),
                     labels = c("<= 17", "17 < qsec <= 19", "> 19"))