Text annotations in R with text and mtext functions

Sample data

The data used in the examples below is the following:

# Data
set.seed(123)
x <- 1:50
y <- x + rnorm(50, sd = 10)
groups <- sample(letters, 50, replace = TRUE)

The `text` function

Adding text

You can add texts to base R plots with the text function. You just need to pass the coordinates and the text you want to add.

plot(x, y, pch = 19, col = 4)
text(x = 10, y = 50, # Coordinates
     label = "Text annotation")

Adding text in R with the text function

Text customization

The added text can be customized with the graphical parameters, such as col, for the color, font for the font style or cex for the text size.

plot(x, y, pch = 19, col = 4)
text(x = 15, y = 50, label = "Text annotation",
     col = "red",   # Color of the text
     font = 2,      # Bold face
     cex = 1.5)     # Size

Plot text customization in R

Text rotation

You can also rotate the text setting a degree or rotation with the srt argument.

plot(x, y, pch = 19, col = 4)

# Rotate 45 degrees
text(x = 15, y = 50, label = "Text annotation",
     srt = 45) # Rotation

Plot text annotation rotation in R

Text splitting

Finally, it is worth to mention that you can split the text in several lines with "\n".

plot(x, y, pch = 19, col = 4)

# Split the text in several lines
text(x = 15, y = 50,
     label = "Text\n annotation") # Split text

Split text annotation in R

Label points

Labelling data points in R

If you have a grouping variable you can pass it to the labels argument of the text function to label the observations. You can set the position specifying the variables and fine-tuning them.

plot(x, y, pch = 19, col = 4,
     ylim = c(-10, 70)) # Change axis limits
text(x = x, y = y - 3,  # Fine-tune the position
     label = groups)

The `mtext` function

The mtext function can be used to add text to all sides of a plot, which can be specified using the side argument.

side	Position
1	bottom
2	left
3	top
4	right

Bottom text

plot(x, y, pch = 19, col = 4)

# Bottom-center
mtext("Bottom text", side = 1)

Bottom text with mtext function

Left text

plot(x, y, pch = 19, col = 4)

# Left-center
mtext("Left text", side = 2)

Left text using mtext function

Top text

plot(x, y, pch = 19, col = 4)

# Top-center
mtext("Top text", side = 3)

Top text with mtext function

Right text

plot(x, y, pch = 19, col = 4)

# Right-center
mtext("Right text", side = 4)

Text on the right with mtext R function

`mtext` adjustment

There are several arguments that you can customize. The most relevant are:

line, to set the margin line where to set the text. Default value is 0.
adj, to adjust the text in the reading direction from 0 to 1 (default value is 0.5).
at, to indicate where to draw the text based on the corresponding axis.
Other graphical parameters related to texts such as col, cex, family and font.

Side and adjustment of mtext in R

Top-right text

plot(x, y, pch = 19, col = 4)

# Top-right text
mtext("Top-right text",
      side = 3, adj = 1)

line argument of the mtext function

Top-center text, line 3

plot(x, y, pch = 19, main = "Title", col = 4)

# Top text, line 3 (over the title)
mtext("Top text line 3",
      side = 3, line = 3)

Adding several lines of text with mtext

Top-right text, lines 0, 1, 2, 3

plot(x, y, pch = 19, main = "Title", col = 4)

mtext("Top-right, line 0",
      side = 3, adj = 1, line = 0)
mtext("Top-right, line 1",
      side = 3, adj = 1, line = 1)
mtext("Top-right, line 2",
      side = 3, adj = 1, line = 2)
mtext("Top-right, line 3",
      side = 3, adj = 1, line = 3)

mtext to the left on the second line

Left text at 50, line 2

plot(x, y, pch = 19, col = 4)

# Left text, line 2, centered at 50
mtext("Left text at 50, line 2",
      side = 2, at = 50, line = 2)

mtext does not support rotation, only horizontal adjustment with las = 1 for the vertical axis and vertical adjustment with las = 3 for the X-axis. If you need to rotate the text you can use text function with srt argument instead.