Cars example

From statmethods.net.

# ggplot2 examples
library(ggplot2)
#use color brewer as default discrete colors
scale_colour_discrete <- function(...) scale_color_brewer(palette="Set1", ...)
scale_fill_discrete <- function(...) scale_fill_brewer(palette="Set1", ...)

data('mtcars')
# create factors with value labels
mtcars$gear <- factor(mtcars$gear,levels=c(3,4,5),
     labels=c("3gears","4gears","5gears"))
mtcars$am <- factor(mtcars$am,levels=c(0,1),
     labels=c("Automatic","Manual"))
mtcars$cyl <- factor(mtcars$cyl,levels=c(4,6,8),
   labels=c("4cyl","6cyl","8cyl"))
head(mtcars)
##                    mpg  cyl disp  hp drat    wt  qsec vs        am   gear
## Mazda RX4         21.0 6cyl  160 110 3.90 2.620 16.46  0    Manual 4gears
## Mazda RX4 Wag     21.0 6cyl  160 110 3.90 2.875 17.02  0    Manual 4gears
## Datsun 710        22.8 4cyl  108  93 3.85 2.320 18.61  1    Manual 4gears
## Hornet 4 Drive    21.4 6cyl  258 110 3.08 3.215 19.44  1 Automatic 3gears
## Hornet Sportabout 18.7 8cyl  360 175 3.15 3.440 17.02  0 Automatic 3gears
## Valiant           18.1 6cyl  225 105 2.76 3.460 20.22  1 Automatic 3gears
##                   carb
## Mazda RX4            4
## Mazda RX4 Wag        4
## Datsun 710           1
## Hornet 4 Drive       1
## Hornet Sportabout    2
## Valiant              1

Kernel density plots for mpg

Grouped by number of gears (indicated by color).
qplot(mpg, data=mtcars, geom="density", fill=gear, alpha=I(.5),
   main="Distribution of Gas Milage", xlab="Miles Per Gallon",
   ylab="Density")

Scatterplot of mpg vs. hp

For each combination of gears and cylinders in each facet, transmission type is represented by shape and color.
qplot(hp, mpg, data=mtcars, shape=am, color=am,
   facets=gear~cyl, size=I(3),
   xlab="Horsepower", ylab="Miles per Gallon")

Regressions of mpg on weight

Separate for each number of cylinders.
ggplot(data = mtcars, aes(x = wt, y = mpg, color = cyl)) + geom_point() +
  geom_smooth(method="lm") +
  labs(main="Regression of MPG on Weight",
   xlab="Weight", ylab="Miles per Gallon")

Boxplots of mpg by number of gears

Observations (points) are overlayed and jittered.
qplot(gear, mpg, data=mtcars, geom=c("boxplot", "jitter"),
   fill=gear, main="Mileage by Gear Number",
   xlab="", ylab="Miles per Gallon")
Author: Jim Hester Created: 2013 Mar 20 10:57:07 AM Last Modified: 2015 Dec 16 09:27:30 AM