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The Green Lab - [12-A] Data visualization in R

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This presentation is about a lecture I gave within the "Green Lab" course of the Computer Science master, Software Engineering and Green IT track of the Vrije Universiteit Amsterdam: http://masters.vu.nl/en/programmes/computer-science-software-engineering-green-it/index.aspx
http://www.procaccianti.me

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The Green Lab - [12-A] Data visualization in R

  1. 1. 1 Het begint met een idee Data Visualization in R Giuseppe Procaccianti
  2. 2. Vrije Universiteit Amsterdam 2 Giuseppe Procaccianti / S2 group / The Green Lab Data Visualization in R ● Goals for this lab session: ○ learn the basics of the ggplot2 package ■ understand the basic concepts behind ggplot2 ■ perform a simple tutorial
  3. 3. Vrije Universiteit Amsterdam 3 Giuseppe Procaccianti / S2 group / The Green Lab A ggplot2 graph
  4. 4. Vrije Universiteit Amsterdam 4 Giuseppe Procaccianti / S2 group / The Green Lab A ggplot2 graph
  5. 5. Vrije Universiteit Amsterdam 5 Giuseppe Procaccianti / S2 group / The Green Lab A ggplot2 graph ● The ggplot2 package is based upon the graphics grammar (gg) concept [1] ● Complex statistical graphs can be constructed by composing elementary elements or changing their properties [1] Wilkinson, Leland. The grammar of graphics. Springer Science & Business Media, 2006.
  6. 6. Vrije Universiteit Amsterdam 6 Giuseppe Procaccianti / S2 group / The Green Lab Example: a pie chart pie <- ggplot(mtcars, aes(x = factor(1), fill = factor(cyl))) + geom_bar(width = 1, position = "fill", color = "black")
  7. 7. Vrije Universiteit Amsterdam 7 Giuseppe Procaccianti / S2 group / The Green Lab Example: a pie chart pie + coord_polar(theta = "y")
  8. 8. Vrije Universiteit Amsterdam 8 Giuseppe Procaccianti / S2 group / The Green Lab The qplot() function ● The qplot() function allows to create quick graphs ● Simple 1-line syntax, but not very powerful - similar to plot() qplot(CPUusr, Watts, data=run)
  9. 9. Vrije Universiteit Amsterdam 9 Giuseppe Procaccianti / S2 group / The Green Lab The ggplot() function ● The ggplot() function is the main function of ggplot ● It allows to create graphs by adding subsequent layers ● Three main layers: aesthetics, geometrics, statistics
  10. 10. Vrije Universiteit Amsterdam 10 Giuseppe Procaccianti / S2 group / The Green Lab The ggplot() function ● The aesthetics layer contains the data you want to encode as graphical properties ● The geometrics layer contains the actual graphical elements a_graph <- ggplot(data = run, aes(x = Watts, y = CPUusr)) a_graph <- a_graph + geom_point() ● The statistics layer contains statistics computed from the data a_graph <- a_graph + stat_smooth()
  11. 11. Vrije Universiteit Amsterdam 11 Giuseppe Procaccianti / S2 group / The Green Lab Example: the violin plot ● From a boxplot…. a_graph <- ggplot(data = run, aes(x = Watts, y = CPUusr)) + geom_boxplot() +
  12. 12. Vrije Universiteit Amsterdam 12 Giuseppe Procaccianti / S2 group / The Green Lab Example: the violin plot ● ...to a violin plot a_graph <- ggplot(data = run, aes(x = Watts, y = CPUusr)) + geom_violin() +
  13. 13. Vrije Universiteit Amsterdam 13 Giuseppe Procaccianti / S2 group / The Green Lab Why violin plots are great ● More informative (full data distribution is shown) ● You can draw boxplots on them!
  14. 14. Vrije Universiteit Amsterdam 14 Giuseppe Procaccianti / S2 group / The Green Lab Tutorial: qplot() + ggplot() ● Perform a basic exercise using both qplot() and ggplot()... ● ...using real experimental data (similar to yours)
  15. 15. Vrije Universiteit Amsterdam 15 Giuseppe Procaccianti / S2 group / The Green Lab Further links and references ● Official ggplot2 website ● qplot() tutorial - Edwin Chen ● ggplot2() tutorial - Josef Fruehwald ● Wilkinson, Leland. The grammar of graphics. Springer Science & Business Media, 2006. (Amazon)
  16. 16. Vrije Universiteit Amsterdam 16 Giuseppe Procaccianti / S2 group / The Green Lab Thank you! g.procaccianti@vu.nl i.malavolta@vu.nl

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