mtcars ggplot doesn't know how to deal with class numeric

Question

I am just trying to make a simple plot using mtcars and ggplot:

ggplot(data=mtcars, aes(x=mpg,y=hp))+geom_line(mpg,hp,col=cyl)

but I get the error:

ggplot doesnt know how to deal with class numeric

What is going on?

Answer 1

My suggestion is to specify all aesthetics in one place and to coerce cyl to factor for colour coding as categorial variable.

ggplot(data=mtcars, aes(x=mpg, y=hp, colour=factor(cyl))) + geom_line()

will create