How to specify different colors with ggplot

Question

library(ggplot2)
p <- ggplot(mtcars, aes(wt, mpg))
p + geom_point(size=4)

Suppose you have the above scatterplot. How can you speci

Answer 1

Sure it can, although this type of work if probably best suited to working with your data frame before ggplot(). You could use ifelse() like this:

library(ggplot2)

p <- ggplot(mtcars, aes(wt, mpg))
p + geom_point(size = 4, 
               aes(color = ifelse(mpg > 25, "> 25", 
                                  ifelse(mpg > 20, "20-25", "< 20")))) +
  scale_color_manual(values = c("> 25" = "red", "< 20" = "blue", "20-25" = "green"),
                     name = "MPG"  )

You don't need to call guides() to create a title you can pass it to the name = .. argument in scale_color_manual()