Understanding Box Plots and Axis Alignment in R

Introduction to Box Plots

A box plot is a graphical representation of data that displays the distribution of values based on their quartiles. It consists of several components, including the median (middle line), quartiles (boxes), and outliers (points outside the boxes). Box plots are useful for comparing distributions across different groups or datasets.

Axis Alignment in R

When working with box plots in R, it’s common to encounter issues with axis alignment, particularly when rotating labels. In this article, we’ll explore how to adjust the x-axis label position and make both the x-axis and y-axis titles visible.

The Problem with Rotating Labels

The problem arises when using the las parameter (label alignment) in combination with rotated labels. When you rotate labels, their positions change, which can lead to the x-axis title being cut off or obscured by the rotated labels.

with(ana1, boxplot(Time~ana1$B, ylab  = "Infiltration Rate (mm/h) ", xlab ="Burn Treatment", las = 2, par(mar = c(12, 5, 4, 2)+0.1), names = c( "Control" , "Not burned since 1954" , "Long rotation burn" , "Short rotation burn" ) ))

In this example, the las parameter is set to 2, which rotates the labels horizontally. However, when rotated, the x-axis label position changes, making it difficult to see.

Solution: Adjusting Axis Alignment

To solve this problem, you can use the title() function in R to manually draw an axis title and adjust its position using the line parameter.

par(mar = c(12, 4, 4, 1) + 0.1);
with(
    ana1,
    boxplot(Time ~ B, ylab  = "Infiltration Rate (mm/h) ", xlab = "", las = 2, names = c("Control", "Not burned since 1954", "Long rotation burn", "Short rotation burn"))
)
title(xlab = "Burn Treatment", line = 10);

In this revised code:

• We adjust the plot margins using par(mar = ...).
• The boxplot() function call remains unchanged, except for setting the x-axis label to an empty string ("").
• We add a title with the title() function, specifying the x-axis label text and line number (10).

By adjusting the plot margins and using the line parameter in title(), we can make both the x-axis and y-axis titles visible.

Sample Data

To demonstrate this solution, let’s create some sample data:

df <- data.frame(
    'Control' = rnorm(100),
    'Not burned since 1954' = rnorm(100),
    'Long rotation burn' = rnorm(100),
    'Short rotation burn' = rnorm(100)
)

This sample data frame contains four columns: Control, Not burned since 1954, Long rotation burn, and Short rotation burn. Each column represents a dataset with 100 observations.

Update

The following code snippet provides an updated version of the solution:

par(mar = c(12, 4, 4, 1) + 0.1);
with(
    ana1,
    boxplot(Time ~ B, ylab  = "Infiltration Rate (mm/h) ", xlab = "", las = 2, names = c("Control", "Not burned since 1954", "Long rotation burn", "Short rotation burn"))
)
title(xlab = "Burn Treatment", line = 10);

This updated code includes the same adjustments as before: adjusting plot margins and using the line parameter in title() to make both the x-axis and y-axis titles visible.

Conclusion

In this article, we explored the challenges of axis alignment when working with box plots in R. By using the title() function and adjusting the plot margins, you can create beautiful and informative box plots that showcase your data effectively. Remember to play around with the line parameter and adjust plot margins to achieve the desired layout for your specific use case.

Last modified on 2023-08-01