Add text to a plot in R software


To add a text to a plot in R, the text() and mtext() R functions can be used.

Add texts within the graph

The text() function can be used to draw text inside the plotting area. A simplified format of the function is :

text(x, y, labels)
  • x and y: numeric vectors specifying the coordinates of the text to plot
  • labels: a character vector indicating the text to be written

An example is shown below :

d<-head(mtcars)
plot(d[,'wt'], d[,'mpg'], 
     main="Milage vs. Car Weight\n~~~~~~~~~~~~~~~~~~~",
      xlab="Weight", ylab="Miles/(US) gallon",
      pch=19, col="darkgreen")
text(d[,'wt'], d[,'mpg'],  row.names(d),
     cex=0.65, pos=3,col="red") 

R software : Add a text to a plot

Add text in the margins of the graph

The mtext() R function can be used to put a text in one of the four margins of the plot. A simplified format of the function is :

mtext(text, side=3)
  • text : the text to be written
  • side : an integer specifying the side of the plot; Possible values are :
    • 1: bottom
    • 2: left
    • 3: top
    • 4: right

An example is shown below :

plot(1:10, 1:10, 
     main="mtext(...) examples\n~~~~~~~~~~~")
mtext("Magic function", side=3)

R software : Add a text to a plot

Add mathematical annotation to a plot

plot(1:10, 1:10, 
     main="text(...) examples\n~~~~~~~~~~~")
text(4, 9, expression(hat(beta) == (X^t * X)^{-1} * X^t * y))
text(7, 4, expression(bar(x) == sum(frac(x[i], n), i==1, n)))

R software : Add a text to a plot

Infos

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


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