A quick introduction to the ggplot2 R package by Hadley Wickham which implements the Grammar of Graphics paradigm in the R language.

1. Slides adapted/stolen from Garret Grolemund/RStudio’s
Data Visualization Course
ggplot2
Jeff Allen
Quantitative Biomedical Research Center
3.18.13

2. Getting Started
install.packages(c("ggplot2", "hexbin",
"ggmap", "maps", "RColorBrewer",
"scales","ReadImages"))
library(ggplot2)
library(hexbin)
library(ggmap)
library(maps)
library(RColorBrewer)
library(scales)
library(ReadImages)

3. Grammar of Graphics
• Framework for describing visualized data
– Mapping data onto a coordinate system
• Created by Leland Wilkinson

8. Your First ggplot2 Plot
> library(ggplot2)
> head(mpg)
manufacturer model displ year cyl trans drv cty hwy fl class
1 audi a4 1.8 1999 4 auto(l5) f 18 29 p compact
2 audi a4 1.8 1999 4 manual(m5) f 21 29 p compact
3 audi a4 2.0 2008 4 manual(m6) f 20 31 p compact
4 audi a4 2.0 2008 4 auto(av) f 21 30 p compact
5 audi a4 2.8 1999 6 auto(l5) f 16 26 p compact
6 audi a4 2.8 1999 6 manual(m5) f 18 26 p compact

9. Your First ggplot2 Plot
ggplot(data=mpg, aes(x=cty, y=hwy))
+ geom_point()

10. Your First ggplot2 Plot
The
data.frame
to plot
ggplot(data=mpg, aes(x=cty, y=hwy))
+ geom_point()

11. Your First ggplot2 Plot
The
data.frame Aesthetic
to plot Mappings
ggplot(data=mpg, aes(x=cty, y=hwy))
+ geom_point()

12. Your First ggplot2 Plot
The
data.frame Aesthetic
to plot Mappings
ggplot(data=mpg, aes(x=cty, y=hwy))
+ geom_point()
What geom
to use in
plotting

13. Your First ggplot2 Plot
library(ggplot2)
ggplot(data=mpg,
aes(x=cty, y=hwy))
+ geom_point()

14. Improvements
Problem: verbosity
ggplot(data=mpg,
aes(x=cty, y=hwy))
+ geom_point()
ggplot(mpg, aes(cty, hwy))
+ geom_point()

15. Improvements
Problem: Overplotting
Solution: Different geoms
ggplot(mpg, aes(cty, hwy))
+ geom_jitter()

16. Improvements
Problem: Overplotting
Solution: Different geoms
ggplot(mpg, aes(cty, hwy))
+ geom_bin2d()

17. Colors & Groups
ggplot(mpg, aes(cty, hwy,
color=drv))
+ geom_jitter()

18. Colors & Groups
ggplot(mpg,aes(drv, hwy))
+ geom_boxplot()

19. Adding Layers
ggplot(mpg,aes(drv, hwy))
+ geom_jitter()
+ geom_boxplot()

20. Adding Layers
ggplot(mpg, aes(cty, hwy))
+ geom_jitter()
+ geom_smooth()

21. Adding Layers
ggplot(data, aes(TIME, Y, color=GROUP)) +
geom_line() + geom_smooth()

22. Faceting
ggplot(mpg, aes(cty, hwy)) + geom_jitter()
+ facet_grid(drv ~ class)

23. Refining Plots
ggplot(mpg, aes(cty, hwy))
+ geom_jitter()
+ xlab("City MPG")
+ ylab("Hwy MPG")
+ ggtitle("City vs
Highway MPG")

24. Etc.

25. Etc.

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31. Etc.

32. Resources
• http://docs.ggplot2.org/
• Google Group
• ggplot2 Book