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Data Analytics – GGPlot Title, Subtitle and Caption

By on Tuesday, June 15, 2021

GGPLOT TITLE, SUBTITLE AND CAPTION

 

This article describes how to add and change a main title, a subtitle and a caption to a graph generated using the ggplot2 R package. We’ll show also how to center the title position, as well as, how to change the title font size and color.

In this R graphics tutorial, you will learn how to:

  • Add titles and subtitles by using either the function ggtitle() or labs().
  • Add caption to a ggplot and change the position.
  • Split a long title into two lines or more using n as a text separator.
  • Change the font appearance (text size, color and face) of titles and caption. For example, to set a bold ggplot title, use this: p + theme(plot.title = element_text(face = "bold")). The allowed values for the font face include: “plain”, “italic”, “bold” and “bold.italic”.
  • Change title position to the center or to any other locations (left, right). The default ggplot title alignment is not centered. It is on the left. It’s possible to put the title in the middle of the chart by specifying the argument hjust = 0.5 in the function element_text(): p + theme(plot.title = element_text(hjust = 0.5)). The options hjust = 1 and hjust = 0 place titles on the right and the left side of the plot, respectively.

 

Contents:

  • Key ggplot2 R functions
  • Add main title, subtitle and caption
  • Change title and caption style: font size, color and face
  • Center the title position
  • Change caption position
  • Conclusion

 

Key ggplot2 R functions

  • Start by creating a box plot using the ToothGrowth data set:
library(ggplot2)
p <- ggplot(ToothGrowth, aes(x = factor(dose), y = len)) + 
  geom_boxplot()
  • Add titles using one of the following functions:
  • p + ggtitle(“Main title”, subtitle = “My subtitle”)
  • p + labs(title = “Main title”, subtitle = “My subtitle”, caption = “My caption”)
  • Key ggplot2 theme options to change the font of titles and captions:
theme(
  plot.title = element_text(),
  plot.subtitle.title = element_text(),
  plot.caption = element_text()
)

Arguments of the function element_text() includes:

  • color, size, face, family: to change the text font color, size, face (“plain”, “italic”, “bold”, “bold.italic”) and family.
  • lineheight: change space between two lines of text elements. Number between 0 and 1. Useful for multi-line plot titles.
  • hjust and vjust: number in [0, 1], for horizontal and vertical adjustment of titles, respectively.
    • hjust = 0.5: Center the plot titles.
    • hjust = 1: Place the plot title on the right
    • hjust = 0: Place the plot title on the left

Add main title, subtitle and caption

  • Use the function labs()
# Default plot
print(p)

# Add titles
p <- p + labs(title = "Effect of Vitamin C on Tooth Growth",
              subtitle = "Plot of length by dose",
              caption = "Data source: ToothGrowth")
p

  • Alternatively, you can use the function ggtitle() as follow:
p + ggtitle(label = "Effect of Vitamin C on Tooth Growth",
              subtitle = "Plot of length by dose")

If the title is too long, you can split it into two or multiple lines using n. In this case you can adjust the space between text lines by specifying the argument lineheight in the theme function element_text():

p + labs(title = "Effect of Vitamin C on Tooth Growth n in Guinea Pigs")+
  theme(plot.title = element_text(lineheight = 0.9))

Change title and caption style: font size, color and face

  • Key functions: theme() and element_text(color, size, face)
  • Allowed values for font face: “plain”, “italic”, “bold” and “bold.italic”
p + theme(
  plot.title = element_text(color = "red", size = 12, face = "bold"),
  plot.subtitle = element_text(color = "blue"),
  plot.caption = element_text(color = "green", face = "italic")
)

Center the title position

Specify the argument hjust = 0.5 in the function element_text() to put the title in the middle:

p + theme(
  plot.title = element_text(hjust = 0.5),
  plot.subtitle = element_text(hjust = 0.5)
)

Other locations adjustment for titles include:

  • hjust = 1: Place the title on the right
  • hjust = 0: Place the title on the left

Change caption position

As for titles, you can modify the caption position using hjust. For example to place the caption on the plot left side, type this:

p + theme(
  plot.caption = element_text(hjust = 0)
  )

Conclusion

  • Create an example of ggplot:
library(ggplot2)
p <- ggplot(ToothGrowth, aes(x = factor(dose), y = len)) + 
  geom_boxplot()
  • Add titles, subtitles and captions:
# Add titles and a caption
p + labs(title = "Effect of Vitamin C on Tooth Growth",
        subtitle = "Plot of length by dose",
        caption = "Data source: ToothGrowth")+
  theme(
    plot.title = element_text(hjust = 0.5, size = 14),    # Center title position and size
    plot.subtitle = element_text(hjust = 0.5),            # Center subtitle
    plot.caption = element_text(hjust = 0, face = "italic")# move caption to the left
  )

 

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