2  Basic ggplot2

Providing only data will results in a empty plot:

library(ggplot2)
ggplot(data = mtcars)

so add an aesthetic. The plot will still be empty since no geom is added.

ggplot(data = mtcars, mapping = aes(x = mpg, y = disp))

Add a geom to add a layer.

ggplot(data = mtcars, mapping = aes(x = mpg, y = disp)) + 
geom_point()

Add colors based on a variable

ggplot(data = mtcars, mapping = aes(x = mpg, y = disp, colour = as.factor(gear))) + 
geom_point()