1. Visualisation in R
Hadley Wickham
Assistant Professor / Dobelman Family Junior Chair
Department of Statistics / Rice University
July 2010
Sunday, 25 July 2010

2. HE LL O
my name is
Hadley
Sunday, 25 July 2010

3. http://had.co.nz/
vanderbilt-vis
Sunday, 25 July 2010

4. 1. Preview of today
2. About ggplot2
3. More resources
4. Diving in
Sunday, 25 July 2010

5. Fuel economy
Basic graphics
Sunday, 25 July 2010

6. ●
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displ
Sunday, 25 July 2010

7. ●
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● midsize
hwy
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25 ● ● ● ●● ● ● ● ● ● pickup
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displ
Sunday, 25 July 2010

8. Diamond prices
Displaying large data
Sunday, 25 July 2010

9. 4000
3000
count
2000
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0
56 58 60 62 64 66 68 70
depth
Sunday, 25 July 2010

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5000
50 60 70 80 90
table
Sunday, 25 July 2010

11. 15000
count
1000
2000
10000 3000
price
4000
5000
6000
7000
5000
1 2 3 4 5
carat
Sunday, 25 July 2010

12. US baby names
US baby names
Data manipulation and
transformation
Sunday, 25 July 2010

13. 6.4
6.2
6.0
avg_length
sex
boy
girl
5.8
5.6
5.4
1880 1900 1920 1940 1960 1980 2000
year
Sunday, 25 July 2010

14. 0.95
0.90
0.85
sex
prop
boy
0.80 girl
0.75
0.70
1880 1900 1920 1940 1960 1980 2000
year
Sunday, 25 July 2010

15. Polishing your plots
Sunday, 25 July 2010

16. 1. Scales: used to override default
perceptual mappings, and tune
parameters of axes and legends.
2. Themes: control presentation of
non-data elements.
3. Saving your work: to include in
reports, presentations, etc.
Sunday, 25 July 2010

17. Sunday, 25 July 2010

18. ggplot2
Sunday, 25 July 2010

19. About ggplot2
Graphical grammar (domain specific
language), based on “The Grammar of
Graphics” by Leland Wilkinson.
Specify what you want, not how to create it.
Many fiddly details taken care of.
“Instead of spending time making your graph
look pretty, you can focus on creating a graph
that bests reveals the messages in your data.”
Sunday, 25 July 2010

20. Useful resources
http://had.co.nz/ggplot2
http://had.co.nz/ggplot2/book
http://groups.google.com/group/ggplot2
http://learnr.wordpress.com
http://ggplot2.wik.is
Sunday, 25 July 2010

21. Learning a new
language is hard!
Sunday, 25 July 2010

22. Scatterplot basics
install.packages("ggplot2")
library(ggplot2)
?mpg
head(mpg)
str(mpg)
summary(mpg)
qplot(displ, hwy, data = mpg)
Sunday, 25 July 2010

23. Scatterplot basics
install.packages("ggplot2")
library(ggplot2)
?mpg
head(mpg)
In ggplot2, we
str(mpg) always explicitly
summary(mpg) specify the data
qplot(displ, hwy, data = mpg)
Sunday, 25 July 2010

24. ●
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qplot(displ, hwy, data = mpg)
displ
Sunday, 25 July 2010

25. Additional variables
Can display additional variables with
aesthetics (like shape, colour, size) or
facetting (small multiples displaying
different subsets)
Sunday, 25 July 2010

26. ●
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35 ●
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● ● class
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● 2seater
30 ● ● ● ● compact
● ● ● ● ●● ●
● midsize
hwy
● ● ● ● ●
● ● ●● ● ● ● ● ● minivan
● ● ● ●● ● ●● ●● ● ● ● ●
25 ● ● ● ●● ● ● ● ● ● pickup
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● subcompact
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qplot(displ, hwy, colour = class, data = mpg)
displ
Sunday, 25 July 2010

27. ●
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● midsize
hwy
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● ● ● ● ● ●● Legend chosen and
displayed automatically.
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2 3 4 5 6 7
qplot(displ, hwy, colour = class, data = mpg)
displ
Sunday, 25 July 2010

28. Your turn
Experiment with colour, size, and shape
aesthetics.
What’s the difference between discrete or
continuous variables?
What happens when you combine
multiple aesthetics?
Sunday, 25 July 2010

29. Discrete Continuous
Rainbow of Gradient from
Colour
colours red to blue
Linear mapping
Discrete size
Size between radius
steps
and value
Different shape
Shape Doesn’t work
for each
Sunday, 25 July 2010

30. Faceting
Small multiples displaying different
subsets of the data.
Useful for exploring conditional
relationships. Useful for large data.
Sunday, 25 July 2010

31. Your turn
qplot(displ, hwy, data = mpg) +
facet_grid(. ~ cyl)
qplot(displ, hwy, data = mpg) +
facet_grid(drv ~ .)
qplot(displ, hwy, data = mpg) +
facet_grid(drv ~ cyl)
qplot(displ, hwy, data = mpg) +
facet_wrap(~ class)
Sunday, 25 July 2010

32. Summary
facet_grid(): 2d grid, rows ~ cols, . for
no split
facet_wrap(): 1d ribbon wrapped into 2d
Scales argument controls whether
position scales are fixed or free.
Sunday, 25 July 2010

33. What’s the ● ●
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this plot? ● ●
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qplot(cty, hwy, data = mpg)
cty
Sunday, 25 July 2010

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qplot(cty, hwy, data = mpg, geom = "jitter")
cty
Sunday, 25 July 2010

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10 15 20 25 30 35
qplot(cty, hwy, data = mpg, geom = "jitter")
cty
Sunday, 25 July 2010

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2seater compact midsize minivan pickup subcompact suv
qplot(class, hwy, data = mpg)
class
Sunday, 25 July 2010

37. How could ● ●
we improve
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40
this plot? ●
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Brainstorm ●
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30
for 1 minute.
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hwy
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2seater compact midsize minivan pickup subcompact suv
qplot(class, hwy, data = mpg)
class
Sunday, 25 July 2010

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pickup suv minivan 2seater midsize subcompact compact
reorder(class, hwy)
Sunday, 25 July 2010

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Incredibly useful
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pickup suv minivan 2seater midsize subcompact compact
qplot(reorder(class, hwy), hwy, data = mpg)
reorder(class, hwy)
Sunday, 25 July 2010

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pickup suv minivan 2seater midsize subcompact compact
qplot(reorder(class, hwy),reorder(class, hwy) = mpg, geom = "jitter")
hwy, data
Sunday, 25 July 2010

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pickup suv minivan 2seater midsize subcompact compact
qplot(reorder(class, hwy), hwy, data hwy)mpg, geom = "boxplot")
reorder(class, =
Sunday, 25 July 2010

42. ●
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qplot(reorder(class,minivan
pickup suv
hwy), 2seater data = subcompact
hwy, midsize mpg, compact
geom = c("jitter", "boxplot"))
reorder(class, hwy)
Sunday, 25 July 2010

43. Your turn
Read the help for reorder. Redraw the
previously plots with class ordered by
median hwy.
How would you put the jittered points on
top of the boxplots?
Sunday, 25 July 2010

44. Aside: coding strategy
At the end of each interactive session, you
want a summary of everything you did. Two
options:
1. Save everything you did with savehistory()
then remove the unimportant bits.
2. Build up the important bits as you go.
(this is how I work)
Sunday, 25 July 2010

45. Sunday, 25 July 2010

46. This work is licensed under the Creative
Commons Attribution-Noncommercial 3.0 United
States License. To view a copy of this license,
visit http://creativecommons.org/licenses/by-nc/
3.0/us/ or send a letter to Creative Commons,
171 Second Street, Suite 300, San Francisco,
California, 94105, USA.
Sunday, 25 July 2010