How Can I Scale Nested plot_grid to the Same Size in R?

When creating complex visualizations in R, you might want to combine multiple plots into a single layout using the cowplot package's plot_grid() function. However, one common challenge is ensuring that nested plot_grid elements are scaled to the same size, ensuring a consistent and polished presentation. This article will guide you through scaling nested plot_grid to the same size for more refined and aligned visualizations using the R Programming Language.

Why Use plot_grid() for Nested Layouts?

plot_grid() from the cowplot package offers an easy way to arrange multiple plots into a grid. When you have multiple grids within a larger grid (nested plot_grid), maintaining consistent scaling across all plots becomes challenging. Proper scaling ensures that all elements are visually balanced, improving readability and aesthetics.

Setting Up the Environment

First, let's install and load the necessary packages:

# Install cowplot and ggplot2 if you haven't already
install.packages("cowplot")
install.packages("ggplot2")

# Load the libraries
library(cowplot)
library(ggplot2)

To explain how to manage nested plot_grid, let's create some simple ggplot2 plots.

# Create individual ggplot2 plots
plot1 <- ggplot(mtcars, aes(x = wt, y = mpg)) + 
  geom_point() + 
  ggtitle("Plot 1: MPG vs Weight")

plot2 <- ggplot(mtcars, aes(x = wt, y = hp)) + 
  geom_point(color = "blue") + 
  ggtitle("Plot 2: HP vs Weight")

plot3 <- ggplot(mtcars, aes(x = mpg, y = hp)) + 
  geom_point(color = "red") + 
  ggtitle("Plot 3: HP vs MPG")

plot4 <- ggplot(mtcars, aes(x = wt, y = qsec)) + 
  geom_point(color = "green") + 
  ggtitle("Plot 4: Quarter Mile Time vs Weight")

Step 1: Create Nested plot_grid

We can combine plot1 and plot2 into a single plot_grid, and plot3 and plot4 into another. Then, we'll nest these two grids together.

# Create the first plot grid
grid1 <- plot_grid(plot1, plot2, labels = c("A", "B"))

# Create the second plot grid
grid2 <- plot_grid(plot3, plot4, labels = c("C", "D"))

# Combine both grids into one
nested_grid <- plot_grid(grid1, grid2, ncol = 1, labels = "AUTO")
nested_grid 

Output:

The resulting nested_grid combines both grid1 and grid2. However, you might notice that the individual plot sizes in the combined grid do not align perfectly.

Step 2: Scaling Nested plot_grid to the Same Size

To ensure that all nested plots are of the same size, you can use the align and rel_heights or rel_widths arguments.

# Creating the final grid with alignment
aligned_grid <- plot_grid(
  grid1, grid2, 
  ncol = 1, 
  align = "v",        # Aligns vertically
  axis = "tb"         # Aligns the top and bottom axes
)

# Display the aligned grid
print(aligned_grid)

Output:

In this example, align = "v" ensures vertical alignment, and axis = "tb" aligns the top and bottom axes.

Method 2: Using rel_heights or rel_widths for Equal Sizing

You can control the relative height or width of each plot within the grid using the rel_heights or rel_widths argument to ensure consistent scaling.

# Adjusting the plot sizes using rel_heights
scaled_grid <- plot_grid(
  grid1, grid2, 
  ncol = 1, 
  rel_heights = c(1, 1)  # Ensures both grids have the same height
)

# Display the scaled grid
print(scaled_grid)

Output:

rel_heights = c(1, 1): This ensures that grid1 and grid2 occupy equal heights within the combined plot, making them the same size.

Method 3: Using plot_grid() with Fixed Ratios

If you want more control over the dimensions, you can manually adjust the aspect ratio of individual plots:

# Adjust aspect ratio of individual plots before combining
plot1_fixed <- plot1 + theme(aspect.ratio = 1)
plot2_fixed <- plot2 + theme(aspect.ratio = 1)
plot3_fixed <- plot3 + theme(aspect.ratio = 1)
plot4_fixed <- plot4 + theme(aspect.ratio = 1)

# Create grids with adjusted aspect ratios
grid1_fixed <- plot_grid(plot1_fixed, plot2_fixed, labels = c("A", "B"))
grid2_fixed <- plot_grid(plot3_fixed, plot4_fixed, labels = c("C", "D"))

# Combine the fixed aspect ratio grids
fixed_grid <- plot_grid(grid1_fixed, grid2_fixed, ncol = 1, rel_heights = c(1, 1))

# Display the final grid
print(fixed_grid)

Output:

Conclusion

Ensuring that nested plot_grid elements are scaled to the same size in R involves using align, axis, rel_heights, rel_widths, or setting aspect.ratio manually. These methods offer flexibility in achieving consistent and visually appealing layouts. By using these techniques, you can create polished and professional visualizations that are easy to interpret and aesthetically pleasing. Now, you're well-equipped to manage nested plot_grid layouts effectively in R.