Dot-dash plot in lattice

In this week assignment i was prompt to create a visualization graph using one of Professor 

Edward R. Tufte Dot-dash plot in lattice function to compare miles per gallon vs car weight. below is the code and plot graph. 

Code:

x <- mtcars$wt

 y <- mtcars$mpg

xyplot(y ~ x, xlab="Car weight (lb/1000)", ylab="Miles per gallon of fuel",

+        par.settings = list(axis.line = list(col="transparent")),

+        panel = function(x, y,...) { 

+            panel.xyplot(x, y, col=1, pch=16)

+            panel.rug(x, y, col=1, x.units = rep("snpc", 2), y.units = rep("snpc", 2), ...)})