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Flexible, Beautiful,Customizable GraphsUnderstanding ggplot2’s Grammar

Kyle Nickodem

Monday, February 2nd, 2015

Flexible, Beautiful, Customizable Graphs

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Take Home Points

Become aware of the various components thatcomprise a graph

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Understand how ggplot2 uses these components toconstruct a plot

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What is this graphic trying to tellus?

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The Grammar of Graphics

Why is it necessary to understand the grammar?

ggplot2 operates using this grammar1.

It provides us with a process to think about thestructure that underlies statistical grapics

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Data and asthetic mapping

Geometric objects

Scales and coordinate system

Plot annotations and themes

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How does this work in ggplot2?

library(ggplot2)head(diamonds)

## carat cut color clarity depth table price x y z## 1 0.23 Ideal E SI2 61.5 55 326 3.95 3.98 2.43## 2 0.21 Premium E SI1 59.8 61 326 3.89 3.84 2.31## 3 0.23 Good E VS1 56.9 65 327 4.05 4.07 2.31## 4 0.29 Premium I VS2 62.4 58 334 4.20 4.23 2.63## 5 0.31 Good J SI2 63.3 58 335 4.34 4.35 2.75## 6 0.24 Very Good J VVS2 62.8 57 336 3.94 3.96 2.48

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ggplot(data=diamonds, aes(x = x, y = carat)) + geom_point()

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ggplot(data=diamonds, aes(x = x, y = carat)) + geom_point()

ggplot() + layer(data = diamonds, mapping = aes(x = x, y = carat), geom = "point", stat = "identity", pos = "identity") scale_x_continuous() + scale_y_continuous() + coord_cartesian() + theme()

ggplot(diamonds, aes(x,carat)) + geom_point()

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Quiz Time

What will this plot look like?

ggplot(data = economics, aes(x = date, y = pop)) + geom_line()

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ggplot(data = economics, aes(x = date, y = pop)) + geom_line()

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Question #2

ggplot(data = diamonds, aes(x = price)) + geom_histogram()

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ggplot(data = diamonds, aes(x = price)) + geom_histogram()

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Add multiple geometric objects

ggplot(data = diamonds, aes(x = price)) + geom_histogram(aes(y = ..density..)) + geom_density(color = "red")

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Frequency of diamond clarity bycut?

ggplot(data=diamonds, aes(x = clarity, fill = cut)) + geom_bar()

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Change color scheme

library(RColorBrewer)ggplot(data=diamonds, aes(x = clarity, fill = cut)) + geom_bar() + scale_fill_brewer()

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Flip the coordinate grid

ggplot(data=diamonds, aes(x = clarity, fill = cut)) + geom_bar() + scale_fill_brewer() + coord_flip()

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Dodged bar chart

ggplot(data=diamonds, aes(x = clarity, fill = cut)) + geom_bar(position = "dodge") + scale_fill_brewer()

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Facet

ggplot(data=diamonds, aes(x = clarity, fill = cut)) + geom_bar() + scale_fill_brewer() + facet_wrap(~cut)

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Alter the theme

ggplot(data=diamonds, aes(x = clarity, fill = cut)) + geom_bar() + scale_fill_brewer() + facet_wrap(~cut) + theme_bw()

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Resources

Hadley's ggplot2 documentation - docs.ggplot2.org

ZevRoss ggplot2 cheatsheet

R Graphics Cookbook

R Color Brewer

Wilkinson, L. (2006). The grammar of graphics. Springer -Available for free from through the UM Library portal.

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Hadley's favorite pie chart

ggplot(df, aes(x = "", y = value, fill = variable)) + geom_bar(width stat = "identity") + scale_fill_manual(values = c("red", "yellow")) + coord_polar("y", start = pi / 3) + labs(title = "Pac man")

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