Graphiques avec ggplot2 - L3 -R3 · TheGrammarOfGraphics Thebasicideatobuildingplot •...

GRAPHIQUES AVEC GGPLOT2L3 -R3

Julie Scholler - B246

novembre 2019

Graphics with ggplot2

Why?• elegant, polyvalent• mature and complete graphics system• very flexible• default behaviour carefully chosen• theme system for polishing plot appearance

How?grammar of graphics (Wilkinson, 2005)

The Grammar Of Graphics

The basic idea to building plot

• specify blocks/layers• combine them• get any kind of graphics

Blocks/layers

• data• aesthetic mapping• geometric object• statistical transformations• scales• coordinate system• position adjustments• faceting

Syntax

ggplot(data=...) + aes(x=..., y=...) + geom_...()

• Data: what is being visualized• Aesthetic Mappings: mappings between variables in the data

and components of the chart• Geometric Objects: geometric objects that are used to display

the data, such as points, lines, or shapes

First try

ggplot(data)

Aesthetic Mapping

In ggplot: aesthetic = “something you can see”

Examples• position (on the x and y axes)• color (“outside” color)• fill (“inside” color)• shape (of points)• linetype• size

Aesthetic mappings are set with the aes() function.

Second try

ggplot(data) + aes(x = note_totale)

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Geometic Objects (geom)

Examples• points: geom_point• lines: geom_line• bar: geom_bar• histogram: geom_histogram• boxplot: geom_boxplot

List of available geometric objectsReference listhelp.search("geom_", package = "ggplot2")

Histogramm

ggplot(data) + aes(x = note_totale) + geom_histogram()

## `stat_bin()` using `bins = 30`. Pick better value with `binwidth`.

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Create Good and Effective Graphics

• Labels+ labs(title=..., subtitle=..., caption=...,

x=..., y=..., color=..., etc.)

• Annotations+ geom_text()+ geom_text_repel()

• Coordinate+ coord_flip()

• Scales, Guides, Themes• Interactivity

ggplot(data = data) + aes(x=note_totale) +geom_histogram(bins = 15, fill="aquamarine3",

col="white") +labs(title = "Distribution des notes au QCM",

x = "Note", y = "Effectif")+theme_minimal()

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Distribution des notes au QCM

Themes

The ggplot2 theme system handles non-data plot elements such as

• Axis labels• Plot background• Facet label backround• Legend appearance

Built-in themes include:

• theme_gray() (default)• theme_bw()• theme_classic()

Multivariateggplot(data = data) + aes(x=note_totale, fill=annee) +

geom_histogram(bins = 15, col="white", alpha=0.6) +labs(title = "Distribution des notes au QCM",

x = "Note", y = "Effectif") + theme_minimal()

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Distribution des notes au QCM

Faceting

• Creates separate graphs for subsets of data• Two solutions

1. facet_wrap(): subsets as the levels of a single groupingvariable

2. facet_grid(): subsets as the crossing of two groupingvariables

• Facilitates comparison among plots

Syntax

ggplot(data=...) + aes(x=..., y=...,fill=...,color=...,group=...) +

geom_...() + facet_...(...) +labs(...) + theme_minimal()

• Data: what is being visualized• Aesthetic Mappings: mappings between variables in the data

and components of the chart• Geometric Objects: geometric objects that are used to display

the data, such as points, lines, or shapes• Statistical Transformations: applied to the data to summarize it• Facets: describe how the data is partitioned into subsets and

how these different subsets are plotted

Base histogram

gg <- ggplot(data = data) +aes(x=note_totale, fill=annee) +geom_histogram(bins = 15, alpha=0.6, col = "white") +labs(title = "Distribution des notes au QCM",

x = "Note", y = "Effectif") +theme_minimal()

facet_wrap()

gg + facet_wrap(~annee)

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Distribution des notes au QCM

Legend position

gg + facet_wrap(~annee) +theme(legend.position="bottom")

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Distribution des notes au QCM

Other use of facet_wrap()

gg + facet_wrap(~annee, ncol=2)

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Distribution des notes au QCM

Use of facet_grid()

gg + facet_grid(annee~sexe)

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Distribution des notes au QCM

Density chartggplot(data = data) + aes(x=note_totale) +

geom_density(fill="aquamarine3", color="white",alpha = 0.6) +

labs(title = "Distribution des notes au QCM",x = "Note", y = "") + theme_minimal()

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Distribution des notes au QCM

Density chartsggplot(data = data) +

aes(x=note_totale, fill=annee, color=annee) +geom_density(alpha = 0.6) +labs(title = "Distribution des notes au QCM",

x = "Note", y = "") + theme_minimal()

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Distribution des notes au QCM

With ridges lineslibrary(ggridges)ggplot(data = data) +

aes(x=note_totale, fill=annee, col=annee, y=annee) +geom_density_ridges(alpha = 0.6, scale = 3) +labs(title = "Distribution des notes au QCM",

x = "Note", y = "") + theme_minimal()

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Distribution des notes au QCM

Bar charts

ggplot(data) + aes(x=annee) +geom_bar(fill="aquamarine3") +theme_minimal()

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Bar charts

ggplot(data) + aes(x=annee) +geom_bar(fill="aquamarine3", width = 0.5) +theme_minimal()

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Bar charts

ggplot(data) + aes(x=annee, fill=bac) +geom_bar(width = 0.5) + theme_minimal()

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bac

Bac ES

Bac S

Bac L

Bac STMG

Bac professionnel

Bar charts

ggplot(data) + aes(x=annee,fill=bac) +geom_bar(width = 0.5,position="fill") + theme_minimal()

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bac

Bac ES

Bac S

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Bac STMG

Bac professionnel

Bar charts

ggplot(data) + aes(x=annee,fill=bac) +geom_bar(width = 0.5, position="dodge") + theme_minimal()

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bac

Bac ES

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Bac STMG

Bac professionnel

Position adjustement

Inside geom

• identity• stack• fill• dodge: side by side• jitter: useful for points (geom_jitter())• nudge: shift points

Draw multiple plots within one figure

density <- ggplot(data = data) +aes(x=note_totale, fill=annee, col=annee) +geom_density(alpha = 0.6) +labs(title = "Notes au QCM",

subtitle = "Les L2 sont très moyens.",x = "Note", y = "")+

theme_minimal()

barplot <- ggplot(data) + aes(x=annee, fill = bac) +geom_bar(width = 0.5) +labs(title = "Séries de baccalauréat par année de Licence",

subtitle = "Les filières ES et S sont très majoritaires.",x = "Note", y = "") +

theme_minimal()

Draw multiple plots within one figure

library(ggpubr)ggarrange(density,barplot,align="h")

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Les L2 sont très moyens.

Notes au QCM

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bac

Bac ES

Bac S

Bac L

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Bac professionnel

Les filières ES et S sont très majoritaires.

Séries de baccalauréat par année de Licence