Scatter Plots - R Graphics - page 136

See Also
For more about overplotting, see Dealing with Overplotting .

Labeling Points in a Scatter Plot

Problem
You want to add labels to points in a scatter plot.

Solution
For annotating just one or a few points, you can use annotate() or geom_text() . For this ex-
ample, we'll use the countries data set and visualize the relationship between health expendit-
ures and infant mortality rate per 1,000 live births. To keep things manageable, we'll just take the
subset of countries that spent more than $2000 USD per capita:

library(gcookbook) # For the data set
subset(countries, Year == 2009 & healthexp > 2000 )

Name Code Year GDP laborrate healthexp infmortality
Andorra AND 2009

NA NA 3089.636 3.1

Australia AUS 2009 42130.82 65.2 3867.429 4.2

Austria AUT 2009 45555.43 60.4 5037.311 3.6

...
United Kingdom GBR 2009 35163.41 62.2 3285.050 4.7

United States USA 2009 45744.56 65.0 7410.163 6.6

We'll save the basic scatter plot object in sp and add then add things to it. To manually add
annotations, use annotate() , and specify the coordinates and label ( Figure 5-30 , left). It may
require some trial-and-error tweaking to get them positioned just right:

sp <- ggplot(subset(countries, Year == 2009 & healthexp > 2000 ),
aes(x = healthexp, y = infmortality)) +
geom_point()

sp + annotate( "text" , x = 4350 , y = 5.4 , label = "Canada" ) +
annotate( "text" , x = 7400 , y = 6.8 , label = "USA" )