Scatter Plots - R Graphics - page 104

See Also
For more on using different colors, see Chapter 12 .
For more information about recoding a continuous variable to a categorical one, see Recoding a
Continuous Variable to a Categorical Variable .

Mapping a Continuous Variable to Color or Size

Problem
You want to represent a third continuous variable using color or size.

Solution
Map the continuous variable to size or colour . In the heightweight data set, there are many
columns, but we'll only use four of them in this example:

library(gcookbook) # For the data set

# List the four columns we'll use
heightweight[, c( "sex" , "ageYear" , "heightIn" , "weightLb" )]

sex ageYear heightIn weightLb
f

11.92 56.3 85.0

f 12.92 62.3 105.0

f 12.75 63.3 108.0

...

m 13.92 62.0 107.5

m 12.58 59.3 87.0

The basic scatter plot in Making a Basic Scatter Plot shows the relationship between the con-
tinuous variables ageYear and heightIn . To represent a third continuous variable, weightLb ,
we must map it to another aesthetic property. We can map it to colour or size , as shown in
Figure 5-9 :

ggplot(heightweight, aes(x = ageYear, y = heightIn, colour = weightLb)) + geom_point()

ggplot(heightweight, aes(x = ageYear, y = heightIn, size = weightLb)) + geom_point()