Understanding ggplot and ggsave: A Deep Dive into Plot Size

When working with R’s popular visualization library, ggplot2, it’s common to encounter the challenge of maintaining a consistent plot size across different devices. The ggsave function allows users to save plots in various formats, but its size parameters can sometimes cause visual inconsistencies. In this article, we’ll explore the use of the egg package and its set_panel_size function to achieve consistent plot sizes with both ggplot2 and ggsave.

Introduction to ggplot2

ggplot2 is a powerful data visualization library built on top of the R language. It’s designed to create high-quality, publication-ready graphics using a grammar-inspired syntax. The library consists of several key components:

• Layers: These are the individual elements that make up a plot, such as points, lines, and shapes.
• Aesthetics: These define the mapping between variables and visual properties like color, shape, and size.

Understanding ggsave

ggsave is another R package used to save ggplot2 plots in various formats. While it provides flexibility when saving plots, its size parameters can sometimes cause issues with plot scaling. The ggsave function takes several arguments, including:

• width: Specifies the width of the saved plot.
• height: Specifies the height of the saved plot.
• unit: Can be set to various units (e.g., cm, in, mm).

The Issue with ggplot2 and ggsave

When using both ggplot2 and ggsave, it’s common to encounter issues with plot size consistency. This can occur due to differences in how the two functions handle aspect ratios and scaling.

Here’s an example code snippet that demonstrates this issue:

library(ggplot2)
library(gridExtra)

ggplot(mtcars, aes(mpg, disp)) + geom_point() +
  labs(title="Rocket science title that will get cut by ggsave")

# To view the plot
gridExtra::grid.arrange(egg::set_panel_size(p=ggplot(mtcars, aes(mpg,disp))+
                                              geom_point()+
                                              labs(title="Rocket science title that will get cut by ggsave"), 
                                             width=unit(5, "cm"), height=unit(7, "cm")))

# To save the plot
ggsave(filename = "myplot.pdf", plot = ggplot(mtcars, aes(mpg,disp))+
      geom_point()+
      labs(title="Rocket science title that will get cut by ggsave"),
      width=unit(5, "cm"), height=unit(7, "cm"))

In this example, the ggplot function is used to create a plot, and then its size is manipulated using both gridExtra::grid.arrange (for viewing) and ggsave. However, as expected, when saved with ggsave, the plot’s size appears distorted compared to its original state.

Solution: Using egg for Consistent Plot Size

To solve this issue, we can utilize the egg package, which provides a more robust way to handle panel sizes in ggplot2. The set_panel_size function from this package allows us to define the dimensions of individual panels within a plot.

Here’s how you can modify our previous example to use egg:

library(ggplot2)
library(egg)

ggplot(mtcars, aes(mpg, disp)) + geom_point() +
  labs(title="Rocket science title that will get cut by ggsave")

# To view the plot
p <- ggplot(mtcars, aes(mpg,disp))+
      geom_point()+
      labs(title="Rocket science title that will get cut by ggsave")
gridExtra::grid.arrange(egg::set_panel_size(p=p, width=unit(5, "cm"), height=unit(7, "cm")))

# To save the plot
ggsave(filename = "myplot.pdf", plot = egg::set_panel_size(p=p, width=unit(5, "cm"), height=unit(7, "cm")))

In this revised example, we first create our ggplot using ggplot. Then, when viewing or saving the plot, we apply the set_panel_size function from egg to define the dimensions of the panel. This ensures that the aspect ratio is preserved, resulting in a more consistent size across different views.

Additional Considerations

Here are some additional considerations and best practices for using egg with ggplot2:

• Aspect Ratio Preservation: When working with plots that involve multiple panels (e.g., multi-panel plots), ensure you use the same aspect ratio for all panels to maintain consistency.
• Unit Conversion: The set_panel_size function allows specifying dimensions in various units. Make sure you’re using compatible units when defining panel sizes to avoid issues during plotting or saving.
• Interactive Plots: When creating interactive plots, it’s a good idea to define the aspect ratio and size of individual panels within the plot frame.

By following these guidelines and techniques for working with egg and ggplot2, you can achieve consistent plot sizes across different views, ensuring high-quality visualizations in your R projects.

Last modified on 2024-11-12