R-Graphics

Stephen Opiyo

2

Basic Graphs

• One of the main reasons data analysts turn to R is for its strong graphic capabilities.

• R generates publication-ready figures.

• "graphics" library loads by default when R is started.

• Ready to go as soon as R opens.

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Graphing basics

Plotting commands1. High-level functions: Create a new plot on the

graphics device

2. Low-level functions: Add more information to an already existing plot, such as extra points, lines, and labels

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Common high-level functions

• plot(): A generic function that produces a type of plot that is dependent on the type of the first argument.

• hist(): Creates a histogram of frequencies

• barplot(): Creates a histogram of values

• boxplot(): Creates a boxplot

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Example 1

• Download data D2_Data_1

• Open file D2_Example_1.R

• R dataset mtcars

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Lower level graphical functions

pch (plotting characters)=“ ” : character or numbers col (color) = “ ” : character or numbers lty = numbers lwd = numbers axes = “L”: L= F, T xlab =“string”, ylab=“string” sub = “string”, main =“string” xlim = c(lo,hi), ylim= c(lo,hi)

cex controls the symbol size in the plot, default is cex=1,

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plot type description: type= " "

p = points

l = lines

o = over plotted points and lines

b, c = points (empty if "c") joined by lines

s = stair steps

h = histogram-like vertical lines

n = does not produce any points or lines

Lower level graphical functions

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Lower-level graphing functions

• pch=0,square• pch=1,circle• pch=2,triangle point up• pch=3,plus• pch=4,cross• pch=5,diamond• pch=6,triangle point down• pch=7,square cross• pch=8,star• pch=9,diamond plus• pch=10,circle plus• pch=11,triangles up and down• pch=12,square plus• pch=13,circle cross• pch=14,square and triangle down• pch=15, filled square blue• pch=16, filled circle blue• pch=17, filled triangle point up blue• pch=18, filled diamond blue• pch=19,solid circle blue• pch=20,bullet (smaller circle)• pch=21, filled circle red• pch=22, filled square red• pch=23, filled diamond red• pch=24, filled triangle point up red• pch=25, triangle point down red

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Lower-level graphing functions

0 5 10 15 20 25

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10

15

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25 pch = symbol types

col = color types

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34

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910

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1920

2122

2324

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Symbol shapes and colors

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Lower-level graphing functions

• Adding text

text()

text(x,y, “text”, options)

points() add some more points to the graph

points(x,y, options)

Saving graphs in Rstudio

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Example 2

• Download data D2_Data_2

• Open file D2_Example_2.R

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Making a histogram

• Make histograms with varying the number of bars (also called ‘bins’ or ‘cells’), e.g. simdata <-rchisq(100,8)hist(simdata) # default number of bins

Setting your own breakpoints

bps <- c(0,2,4,6,8,10,15,25)

hist(simdata,breaks=bps)

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3-dimensional Scatterplots

• Need a package scatterplot3d

• Install package scatterplot3d using install.packages("scatterplot3d") command

• Alternatively install using Rstudio using Packages

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Multiple graph on one page

• Combining multiple plots using par () and mfrow = c(nrows, ncols) to create a matrix of nrows by ncols

• ?par• par(mfrow=c(1,2))

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Exercise

0 5 10 15 20 25

05

10

15

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25 pch = symbol types

col = color types

12

34

56

78

910

1112

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1516

1718

1920

2122

2324

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par(mfrow=c(3,5))plot(D2_Data_2[,2], D2_Data_2[,3], type="p", pch=1, col="1", xlab ="Peak1", ylab ="Peak2", main="Plot of Peak1 vs Peak2", font.main =1)

Replace pch=1 and col =1 with 2 to 15: Export the graph and save it as Day_2_Graph.pdf