You want to create a scatter plot.

To make a scatter plot (Figure 2-1), use plot() and pass it a vector of x values followed by a vector of y values:

plot(mtcars$wt, mtcars$mpg)

Figure 2-1. Scatter plot with base graphics

With the ggplot2 package, you can get a similar result using qplot() (Figure 2-2):

library(ggplot2)
qplot(mtcars$wt, mtcars$mpg)

Figure 2-2. Scatter plot with qplot() from ggplot2

If the two vectors are already in the same data frame, you can use the following syntax:

qplot(wt, mpg, data=mtcars)
# This is equivalent to:
ggplot(mtcars, aes(x=wt, y=mpg)) + geom_point()

See Chapter 5 for more in-depth information about creating scatter plots.