Intro to ggplot2. Hadley Wickham. Assistant Professor / Dobelman Family Junior Chair Department of Statistics / Rice University

Transcription

1 Intro to ggplot2 Hadley Wickham Assistant Professor / Dobelman Family Junior Chair Department of Statistics / Rice University November 2010

2 HELLO my name is Hadley

3 had.co.nz/courses/ 10-tokyo

4 Outline

5 Data analysis is the process by which data becomes understanding, knowledge and insight

6 Understand Visualise Access Transform Model Communicate

7 Understand Visualise Access Transform Model Communicate

8 displ hwy class 2seater compact midsize minivan pickup subcompact suv

9 count depth

10 15000 price count carat

11 George Georgia prop Georgie sex boy girl 4e 04 3e 04 2e 04 1e year

12 prop 0.80 sex boy girl year

13 diff abs(mean) Angel Bernice Billie Bonnie Carol Cecil Charles Charlie Clyde Connie Dale Dana David Eddie Elizabeth Frances Francis Frank Gail Gene George Hazel Helen Henry Ira Jackie James Jamie Jean Jerry Jesse Jessie Jimmie Joe John Johnnie Joseph June Kelly Lee Leslie Lynn Margaret Marion Mary Michael Ollie Ora Patsy Pearl Ray Richard Robert Robin Ruby Shannon Shirley Sidney Terry Thomas Tracy William Willie

14 Plotting basics

15 Learning a new language is hard!

16 Scatterplot basics install.packages("ggplot2") library(ggplot2)?mpg head(mpg) str(mpg) summary(mpg) Always explicitly specify the data qplot(displ, hwy, data = mpg)

17 displ hwy qplot(displ, hwy, data = mpg)

18 Additional variables Can display additional variables with aesthetics (like shape, colour, size) or facetting (small multiples displaying different subsets)

19 displ hwy class 2seater compact midsize minivan pickup subcompact suv Legend chosen and displayed automatically. qplot(displ, hwy, colour = class, data = mpg)

20 Your turn Try mapping different variables to the colour, size, and shape aesthetics. Is there a difference between discrete and continuous variables? What happens when you use multiple aesthetics?

21 Aside: workflow Keep a copy of the slides open so that you can copy and paste the code. For complicated commands, write them in the script editor and then copy and paste.

22 Discrete Continuous Colour Rainbow of colours Gradient from red to blue Size Discrete size steps Linear mapping between radius and value Shape Different shape for each Doesn t work

23 Faceting Small multiples displaying different subsets of the data. Useful for exploring conditional relationships. Useful for large data.

24 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)

25 Summary facet_grid(): 2d grid, rows ~ cols,. for no split facet_wrap(): 1d ribbon wrapped into 2d

26 cty hwy qplot(cty, hwy, data = mpg) What s the problem with this plot?

27 cty hwy qplot(cty, hwy, data = mpg, geom = "jitter") geom controls type of plot

28 class hwy seater compact midsize minivan pickup subcompact suv qplot(class, hwy, data = mpg) How could we improve this plot? Brainstorm for 1 minute.

29 reorder(class, hwy) hwy pickup suv minivan 2seater midsize subcompact compact qplot(reorder(class, hwy), hwy, data = mpg) Incredibly useful technique!

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

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

32 reorder(class, hwy) hwy pickup suv minivan 2seater midsize subcompact compact qplot(reorder(class, hwy), hwy, data = mpg, geom = c("jitter", "boxplot"))

33 Your turn Read the help for reorder. Redraw the previous plots with class ordered by median hwy. How would you put the jittered points on top of the boxplots?

34

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