The legends in ggplot2 are automatically generated based on various aesthetics such as color, fill, size, and shape. There might be some instances when you are required to customize the legend’s appearance (e.g., change text size, position, background, or spacing) without making any changes in the main plot.
In this blog, we are about to explore various ways to control ggplot2 legend look without affecting the plot along with understanding the legends present in ggplot2.
Table of Content
What are Legends in ggplot2
In ggplot2, a legend is a guide that explains the meaning of visual elements like colors, shapes, or sizes used in a plot. The legends are linked to aesthetic mapping such as color = variable, whichwillcreate a legend for various colors, fill = variable will create a legend for filled areas and size = variable will create a legend for different point sizes.
You can also modify the legend appearance by using the theme() function without making any changes in the plot’s data visualization.
How to Control ggplot2 Legend Look Without Affecting the Plot?
Let’s see how we can control different legend components.
1. Change Legend Title
You can use the labs() function to rename the legend title.
library(ggplot2)
# Sample plot
a <- ggplot(mtcars, aes(x = wt, y = mpg, color = factor(cyl))) +
geom_point(size = 3) +
labs(color = "Cylinders")
a
Output:
2. Modify Legend Labels
You can use scale_color_manual() or scale_fill_manual() to rename legend labels.
For example:
a + scale_color_manual(values = c("purple", "blue", "green"),
labels = c("5-Cylinder", 7-Cylinder", "9-Cylinder"))
Output:
3. Modify Legend Position
Now, if you want to reposition the legend without making any changes in the plot, you can do so by using the theme() function.
3.1. Move Legend to the Bottom
p + theme(legend.position = "bottom")
3.2 Move Legend to the Top
a + theme(legend.position = "top")
3.3 Move Legend Inside the Plot
To place the legend inside the plot, you can use(x, y) coordinates.
a + theme(legend.position = c(0.8, 0.2))
4. Customize Legend Appearance
4.1 Adjust Legend Text Size
a + theme(legend.text = element_text(size = 13))
Output:
4.2 Change Legend Background
a + theme(legend.background = element_rect(fill = "lightgray", color = "blue"))
Output:
4.3 Modify Legend Key Size
a + theme(legend.key.size = unit(1.7, "cm"))
Output:
4.4 Adjust Legend Item Spacing
a + theme(legend.spacing.x = unit(0.6, 'cm'),
legend.spacing.y = unit(0.6, 'cm'))
Output:
Remove the Legend While Keeping the Plot Unchanged
If you want to remove the legend but keep the plot the same, use:
a + theme(legend.position = "none")
Output:
Conclusion
You can customize the legends in ggplot2 since it helps get a better visualization along with clarity in the representation of data. Using labs() along with sclae_*_manual() allows you to change legend titles and labels so that the graph can become more readable. A change in legend position without an alteration in the plot itself is possible through the function theme(legend.position = “top”). Moreover, theme() allows you to go a step further and modify parameters such as the size of text, background, and key for an enhanced appearance. These methods will help you refine plots for better communication and aesthetic appeal
FAQs
1. How can I change the legend with no effect on the plot?
You can use theme() settings as: legend.text, legend.background, and legend.position.
2. Can I change the title of the legend without altering the data?
Indeed, you can use labs(color = “New Title”).
3. How can I change the distance between legends?
You will need to use legend.spacing.x and legend.spacing.y in theme().
4. How can I put the legend inside the plot?
Use theme(legend.position = c(x, y)) with values between 0 and 1.
5. How can I suppress the legend but retain the colors?
You can use the theme (legend.position = “none”).