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(0.5), main = "Distribution of Gas Milage", 
    xlab = "Miles Per Gallon", ylab = "Density")

plot of chunk cars_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")

plot of chunk cars_scatter

Regressions of mpg on weight

Separate for each number of cylinders.

qplot(wt, mpg, data = mtcars, geom = c("point", "smooth"), method = "lm", formula = y ~ 
    x, color = cyl, main = "Regression of MPG on Weight", xlab = "Weight", ylab = "Miles per Gallon")

plot of chunk cars_regressions

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")

plot of chunk cars_boxplots

Author: Jim Hester Created: 2013 Mar 20 10:57:07 AM Last Modified: 2013 Oct 16 03:50:50 PM