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Intermediate Data Analysis with R

5 Data Viz with ggplot2, themes

5.1 Built-in Themes

ggplot2 allows you to have fine control over all visual aspects of the plot. The default ggplot2 theme is theme_gray() (or theme_grey() will also work), but you can also choose theme_bw(), which produces a more minimalist plot. You can set the base size of a plot as an argument.


z <- ggplot(mtcars, aes(x = wt, y = mpg, colour = factor(cyl))) +
  geom_point(alpha = 0.6, size = 3, shape = 16) +
  scale_y_continuous("Miles/(US) gallon", 
                     limits = c(10, 40), 
                     breaks = seq(10, 40, 10),
                     expand = c(0,0)) + 
  scale_x_continuous("Weight (lb/1000)",
                     limits = c(1,6), 
                     breaks = 1:6,
                     expand = c(0,0)) +
  scale_colour_brewer("Cylinders")

z
The ggplot2 default theme_gray() and magnified theme_bw().

Figure 5.1: The ggplot2 default theme_gray() and magnified theme_bw(). 

# Black and White theme, with larger base size, shown right:
z + theme_classic(12)

5.2 Custom themes:

You can change individual aspects by modifying the default template, as shown below.


# Custom theme, shown right:
z + theme(rect = element_blank(), 
          axis.ticks = element_line(colour = "#A50F15"),
          axis.text = element_text(colour = "#A50F15"))
An example of updating an individual ggplot with custom theme settings using the `theme()` function.

Figure 5.2: An example of updating an individual ggplot with custom theme settings using the theme() function.

Arguments for the themes layer in ggplot2 v 3.2.1:

Text, modify with element_text()

  • text
    • title
      • legend.title
      • plot.title
      • plot.subtitle
      • plot.caption
      • plot.tag
    • axis.title
      • axis.title.x
        • axis.title.x.top
        • axis.title.x.bottom
      • axis.title.y
        • axis.title.y.left
        • axis.title.y.right
    • axis.text
      • axis.text.x
        • axis.text.x.top
        • axis.text.x.bottom
      • axis.text.y
        • axis.text.y.left
        • axis.text.y.right
    • legend.text
    • strip.text
      • strip.text.x
      • strip.text.y

Lines, modify with element_line()

  • line
    • axis.ticks
      • axis.ticks.x
        • axis.ticks.x.top
        • axis.ticks.x.bottom
      • axis.ticks.y
        • axis.ticks.y.left
        • axis.ticks.y.right
    • axis.line
      • axis.line.x
        • axis.line.x.top
        • axis.line.x.bottom
      • axis.line.y
        • axis.line.y.left
        • axis.line.y.right
    • panel.grid
      • panel.grid.major
        • panel.grid.major.x
        • panel.grid.major.y
      • panel.grid.minor
        • panel.grid.minor.x
        • panel.grid.minor.y

Rect, modify with element_rect()

  • rect
    • legend.background
    • legend.key
    • panel.background
    • panel.border
    • plot.background
    • strip.background
      • strip.background.x
      • strip.background.y

Units, specify with unit()

  • axis.ticks.length
    • axis.ticks.length.x
      • axis.ticks.length.x.top
      • axis.ticks.length.x.bottom
    • axis.ticks.length.y
      • axis.ticks.length.y.left
      • axis.ticks.length.y.right
  • legend.spacing
    • legend.spacing.x
    • legend.spacing.y
  • legend.key.size
    • legend.key.height
    • legend.key.width
  • legend.box.spacing
  • panel.spacing
    • panel.spacing.x
    • panel.spacing.y
  • plot.margin
  • strip.switch.pad.grid
  • strip.switch.pad.wrap

Positioning and sizes

  • aspect.ratio
  • legend.margin
  • legend.text.align
  • legend.title.align
  • legend.position
  • legend.direction
  • legend.justification
  • legend.box
    • legend.box.just
    • legend.box.margin
    • legend.box.background
  • panel.ontop
  • plot.tag.position
  • strip.placement

When creating new themes from scratch:

  • complete, TRUE if this is a complete theme, e.g. theme_grey(). Complete themes behave differently when added to a ggplot object. All elements will be set to inherit from blank elements. Defaults to FALSE.
  • validate, TRUE to run validate_element(), defaults to FALSE.

It’s common to combine your custom theme with a built in theme:

# Custom theme, shown right:
z + theme_classic() +
  theme(rect = element_blank(), 
          axis.ticks = element_line(colour = "#A50F15"),
          axis.text = element_text(colour = "#A50F15"))

Which can also be saved as its own layer:


myTheme <- theme_classic() +
  theme(rect = element_blank(), 
          axis.ticks = element_line(colour = "#A50F15"),
          axis.text = element_text(colour = "#A50F15"))

z + myTheme

5.3 Updating the default theme: 

# Save theme_gray() settings, and make an update:
original <- theme_update(panel.background = element_blank(), 
                         legend.key = element_blank(), 
                         axis.line = element_line(colour = "black"),
                         legend.position = c(.9, .9),
                         panel.grid.major = element_blank(),
                         panel.grid.minor = element_blank(),
                         axis.title.x = element_text(vjust = -0.3),
                         axis.text.x = element_text(colour = "black"),
                         axis.text.y = element_text(colour = "black")
                         )
# Plot with updated theme_gray() theme, shown left
z

# Reset original theme_gray() settings
theme_set(original)
# Plot with original theme_gray() settings, shown right
z