Change Background Color with plot_grid in R

When creating complex visualizations, combining multiple plots into a single figure is often useful. The cowplot package in R provides a convenient function plot_grid() that allows you to combine multiple ggplot2 plots into a grid. However, customizing the background color of the combined plot can be a bit tricky if you're unfamiliar with the process. This guide will show you how to change the background color of the grid created by plot_grid().

Introduction to plot_grid

The plot_grid function allows you to arrange multiple ggplot objects in a grid layout. By default, the background of the entire plot grid inherits the background color from the individual plots. However, you can customize this to create a unified appearance that stands out.

Prerequisites

Before you begin, ensure you have the following packages installed:

library(ggplot2)
library(cowplot)

Now we will discuss step by step implementation of Change Background Color with plot_grid in R Programming Language.

Step 1: Creating Basic Plots Using ggplot2

Before diving into plot_grid, let’s create two simple plots using ggplot2. These plots will later be combined using plot_grid().

# Creating the first plot
plot1 <- ggplot(mtcars, aes(x = wt, y = mpg)) +
  geom_point(color = "blue") +
  theme_minimal() +
  ggtitle("Scatter Plot of mpg vs wt")

# Creating the second plot
plot2 <- ggplot(mtcars, aes(x = cyl, fill = as.factor(cyl))) +
  geom_bar() +
  theme_minimal() +
  ggtitle("Bar Plot of Cylinder Counts")

At this point, you have two individual plots: a scatter plot (plot1) and a bar plot (plot2).

Step 2: Combining Plots Using plot_grid()

The plot_grid() function can combine these two plots into one layout. Here’s how it’s done:

combined_plot <- plot_grid(plot1, plot2, labels = c("A", "B"))
print(combined_plot)

Output:

By default, the combined plot will have a white background. Let's change this.

Step 3: Changing the Background Color Using plot_grid()

To change the background color of the entire grid, you can use the background_color parameter from plot_grid(). Unfortunately, plot_grid() itself does not have a built-in background_color argument. Instead, you can use the ggdraw() function from cowplot to set the background color.

# Using ggdraw() to change the background color
colored_combined_plot <- ggdraw() +
  draw_plot(plot_grid(plot1, plot2, labels = c("A", "B")), 0, 0, 1, 1) +
  theme(plot.background = element_rect(fill = "lightgray", color = NA))

print(colored_combined_plot)

Output:

In this code snippet, the ggdraw() function creates a new plot object with the specified background color (lightgray). You can replace "lightgray" with any color of your choice ( "lightblue", "yellow").

Step 4: Customizing Background Color for Each Individual Plot

You might want to customize the background color for individual plots before combining them. This can be done using theme() within each ggplot2 plot.

# Setting individual plot backgrounds
plot1 <- plot1 + theme(plot.background = element_rect(fill = "lightblue", color = NA))
plot2 <- plot2 + theme(plot.background = element_rect(fill = "lightpink", color = NA))

# Combine the plots with plot_grid
combined_plot_custom_bg <- plot_grid(plot1, plot2, labels = c("A", "B"))
print(combined_plot_custom_bg)

Output:

In this case, plot1 has a light blue background, while plot2 has a light pink background.

Advanced Customization for Adding a Border and Adjusting Margins

You can add borders and adjust margins to enhance your combined plot's visual appeal further.

# Adding a border to the combined plot
final_plot <- ggdraw() +
  draw_plot(plot_grid(plot1, plot2, labels = c("A", "B"), rel_widths = c(1, 1)), 0, 0, 1, 1) +
  theme(
    plot.background = element_rect(fill = "white", color = "black", size = 2),
    plot.margin = margin(10, 10, 10, 10)
  )

print(final_plot)

Output:

• The element_rect() function adds a border (color = "black") around the entire combined plot.
• The plot.margin function sets a margin around the plot (10 units on all sides).

Conclusion

• plot_grid() is a powerful tool from the cowplot package for combining multiple plots into a grid layout.
• While plot_grid() does not have a direct argument for changing background colors, you can leverage ggdraw() and theme() functions to customize the background.
• You can change individual plot backgrounds using theme(plot.background = element_rect(...)).
• Adjusting borders and margins enhances the visual appeal of combined plots.

Changing the background color with plot_grid() in R requires understanding how ggdraw() interacts with the cowplot package. By using the techniques discussed above, you can create visually appealing combined plots with customized background colors that suit your data visualization needs.