Plotting symbols

The different points symbols commonly used in R are shown in the figure below :

The function used to generate this figure is provided at the end of this document

Point can be omitted from the plot using pch = NA.

Examples

x<-c(2.2, 3, 3.8, 4.5, 7, 8.5, 6.7, 5.5)
y<-c(4, 5.5, 4.5, 9, 11, 15.2, 13.3, 10.5)
# Plot points
plot(x, y)
# Change plotting symbol
# Use solid circle
plot(x, y, pch = 19)

By default pch=1

The following arguments can be used to change the color and the size of the points :

• col : color (code or name) to use for the points
• bg : the background (or fill) color for the open plot symbols. It can be used only when pch = 21:25.
• cex : the size of pch symbols
• lwd : the line width for the plotting symbols

# Change color
plot(x, y, pch=19, col="darkgreen", cex=1.5)
# Color can be a vector
plot(x, y, pch=19, col=c("green", "red"))
# change border, background color and line width
plot(x, y, pch = 24, cex=2, col="blue", bg="red", lwd=2)

Note that, only pch from 21 to 25 can be filled using the argument bg=

Other characters can be used to specify pch including “+”, “*“,”-“,”.“,”#, “%”, “o”

set.seed(1234)
plot(x=rnorm(100), y=rnorm(100), pch="+")

R script to generate a plot of point shapes in R

Use the following R function to display a graph of the plotting symbols :

#++++++++++++++++++++++++++++++++++++++++++++
#generate a plot of point shapes which R knows about.
#++++++++++++++++++++++++++++++++++++++++++++
generateRPointShapes<-function(){
  oldPar<-par()
  par(font=2, mar=c(0.5,0,0,0))
  y=rev(c(rep(1,6),rep(2,5), rep(3,5), rep(4,5), rep(5,5)))
  x=c(rep(1:5,5),6)
  plot(x, y, pch = 0:25, cex=1.5, ylim=c(1,5.5), xlim=c(1,6.5), 
       axes=FALSE, xlab="", ylab="", bg="blue")
  text(x, y, labels=0:25, pos=3)
  par(mar=oldPar$mar,font=oldPar$font )
}
generateRPointShapes()

Infos

This analysis has been performed using R (ver. 3.1.0).

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