Axes customization in R

We are going to use the data of the code above on the following examples:

# Reproducible data
set.seed(1)
x <- runif(100, min = -5, max = 5)
y <- x ^ 3 + rnorm(100, mean = 0, sd = 5)

X and Y axis labels

The default axis labels will depend on the function you are using, e.g. plot function will use the names of the input data, boxplot won’t show any axis labels by default and hist will show the name of the variable on the X-axis and “Frequency” or “Density” on the Y-axis, depending on the type of the histogram.

Default plot

For illustration purposes we are going to use the plot function but the examples are extensible to other functions. In order to plot the data we defined before you can type:

plot(x, y, pch = 19)

Default plot in base R

Custom axes labels

In order to change the axis labels you can specify the arguments xlab and ylab as follows:

plot(x, y, pch = 19,
     xlab = "My X-axis label",
     ylab = "My Y-axis label")

Adding axis labels in R

Labels color

In addition, is is possible to modify the color of the axes labels with the col.lab argument.

plot(x, y, pch = 19,
     xlab = "My X-axis label",
     ylab = "My Y-axis label",
     col.lab = 4) # Color of the labels

Axis color labels in R

Remove axis labels

You can remove the axis labels with two different methods:

Remove labels in R

Option 1. Set the xlab and ylab arguments to "", NA or NULL.

# Delete labels
plot(x, y, pch = 19,
     xlab = "", # Also NA or NULL
     ylab = "") # Also NA or NULL

Remove axes labels with ann argument in R

Option 2. Set the argument ann to FALSE. This will override the label names if provided.

# Equivalent
plot(x, y, pch = 19,
     xlab = "My X-axis label",
     ylab = "My Y-axis label",
     ann = FALSE)

The `axis` function

The axis function allows adding axes to all sides of the the current plot, with the possibility of specifying the position and the labels of the tick marks. Recall to type ?axis for further details.

axis	Position
1	below
2	left
3	above
4	right

Option 1. Set xaxt = "n" and yaxt = "n" to remove the tick labels of the plot and add the new labels with the axis function. Note that the at argument sets where to show the tick marks.

plot(x, y, pch = 19,
     xaxt = "n", yaxt = "n")

# X-axis
axis(1, at = c(-4, 0, 4))

# Y-axis
axis(2, at = c(-100, -50, 0, 50, 100))

Adding axes in R with axis function

Option 2. Set axes = FALSE inside your plotting function to remove the plot box and add the new axes with the axis function.

plot(x, y, pch = 19,
     axes = FALSE)

# Add X-axis
axis(1)

# Add Y-axis
axis(2)

# You can add the plot box again
# box()

Add axis to R plot

Color of the axes

You can also customize the color of the axis and the ticks with the col and col.ticks arguments.

plot(x, y, pch = 19,
     axes = FALSE)

# Add X-axis
axis(1,
     col = "blue",        # Axis line color
     col.ticks = "green", # Ticks color
     col.axis = "red")    # Labels color

# Add Y-axis
axis(2,
     col = "blue",
     col.ticks = "green",
     col.axis = "red")

Axis and ticks color customization in R

Axis tick marks

In addition to axes labels, the tick marks of each axis can be customized in different ways.

`xaxp` and `yaxp` arguments

Customize R tick labels position

The xaxp (X-axis) and yaxp (Y-axis) arguments allow customizing where the ticks of each axis start and end and the number of regions to divide the axis specifying vectors of the form c(start, end, number_regions).

plot(x, y, pch = 19,
     xaxp = c(-3, 3, 3),
     yaxp = c(-70, 70, 5))

Minor ticks

Minor ticks in R

It is possible to add minor ticks to the axes with the minor.tick function of the Hmisc library. The function will allow you to specify the tick density, the size and addition arguments to each axis.

# install.packages("Hmisc")
library(Hmisc)

plot(x, y, pch = 19)
minor.tick(nx = 2, ny = 2,   # Ticks density
           tick.ratio = 0.5) # Ticks size

Interior ticks

You can set interior ticks passing positive values to tck argument. The greater the value, the longer the ticks. Default value is tck = -0.5.

# Interior ticks
plot(x, y, pch = 19,
     tck = 0.02)

Interior ticks in R

Rotate tick mark labels

It is possible to rotate the tick mark labels in several ways making use of the las argument.

Rotate tick mark labels in R with las argument

Option 1. Parallel to axis (default).

plot(x, y, pch = 19,
     las = 0,
     main = "Parallel")

Horizontal tick marks in R

Option 2. Horizontal.

plot(x, y, pch = 19,
     las = 1,
     main = "Horizontal")

Perpendicular tick marks in R

Option 3. Perpendicular to axis.

plot(x, y, pch = 19,
     las = 2,
     main = "Perpendicular")

Vertical tick marks in R with las argument

Option 4. Vertical.

plot(x, y, pch = 19,
     las = 3,
     main = "Vertical")

Custom tick mark labels

The labels argument of the axis function allows customizing the tick mark labels.

# Change X-axis tick labels
plot(x, y, pch = 19, xaxt = "n")
axis(1, at = seq(round(min(x)),
                 round(max(x)), by = 1),
     labels = 1:11)

Specifying custom tick marks in R

Note that you can also set texts in addition to numbers, or even expressions.

# X-axis tick labels with text
plot(x, y, pch = 19, xaxt = "n")
axis(1, at = c(-2, 2),
     labels = c("Some text", "Other text"))

Adding text as tick labels in R

Remove tick marks

You can remove the tick marks of one of the two axis or of both at the same time setting arguments xaxt and yaxt to "".

Remove X-axis tick marks in R

Option 1. Remove only X-axis ticks.

# Remove X axis tick labels
plot(x, y, pch = 19,
     xaxt = "n",
     main = "xaxt = 'n'")

Remove Y-axis tick marks in R

Option 2. Remove only Y-axis ticks.

# Remove Y axis tick labels
plot(x, y, pch = 19,
     yaxt = "n",
     main = "yaxt = 'n'")

Remove all tick marks in R

Option 3. Remove both X-axis and Y-axis ticks.

# Remove both axis tick labels
plot(x, y, pch = 19,
     yaxt = "n",
     xaxt = "n",
     main = "xaxt = 'n', yaxt = 'n'")

Remove the axes and the box of a plot in R

Option 4. Remove both X-axis and Y-axis ticks and the box.

# Remove axis tick labels and the box
plot(x, y, pch = 19,
     axes = FALSE,
     main = "axes = FALSE")

Axis limits

The axis limits can be customized with the xlim and ylim arguments for the X and Y axis, respectively.

# Axis limits
plot(x, y, pch = 19,
     xlim = c(0, 4),   # X-axis limits
     ylim = c(0, 100)) # Y-axis limits

Axis limits in R with xlim and ylim arguments

Axis scale

Axis scale in R

Original data.

# Positive data
w <- x[x > 0]
z <- y[y > 0]

# Default
plot(w, z,
     main = "Untransformed")

Log X-axis in R

X-axis transformed.

# Log scale. X-axis
plot(w, z,
     log = "x", 
     main = "X-axis transformed")

Log Y-axis in R

Y-axis transformed.

# Log scale. Y-axis
plot(w, z,
     log = "y",   
     main = "Y-axis transformed")

X and Y axis log in R

Both transformed.

# Log scale. X and Y axis
plot(w, z,
     log = "xy", 
     main = "Both transformed")

Dual axis

You can join together two plots with different Y-axis scale increasing the margins of the plot, using par(new = TRUE), creating a new plot without axis or labels and setting a new axis with the axis function.

# Increase the plot margins
par(mar = c(5, 4, 4, 4) + 0.25)

# Data
plot(x, y, pch = 19, ylab = "Var 1")

# Needed to merge the plots
par(new = TRUE)

# More data
plot(x ^ 2, y ^ 2,
     col = 4, pch = 19,
     axes = FALSE, # No axes
     bty = "n",    # No box
     xlab = "", ylab = "") # No axis labels

# New axis
axis(4)
# Axis label
mtext("Var 2", side = 4, line = 3, col = 4)

Plot with dual axis in R