theme_get: Get, set, and modify the active theme

Description

The current/active theme (see theme()) is automatically applied to every plot you draw. Use theme_get() to get the current theme, and theme_set() to completely override it. theme_update() and theme_replace() are shorthands for changing individual elements.

Usage

theme_get()
theme_set(new)
theme_update(...)
theme_replace(...)
e1 %+replace% e2

Value

theme_set(), theme_update(), and theme_replace()

invisibly return the previous theme so you can easily save it, then later restore it.

Arguments

new: new theme (a list of theme elements)
...: named list of theme settings
e1, e2: Theme and element to combine

Adding on to a theme

+ and %+replace% can be used to modify elements in themes.

+ updates the elements of e1 that differ from elements specified (not NULL) in e2. Thus this operator can be used to incrementally add or modify attributes of a ggplot theme.

In contrast, %+replace% replaces the entire element; any element of a theme not specified in e2 will not be present in the resulting theme (i.e. NULL). Thus this operator can be used to overwrite an entire theme.

theme_update() uses the + operator, so that any unspecified values in the theme element will default to the values they are set in the theme. theme_replace() uses %+replace% to completely replace the element, so any unspecified values will overwrite the current value in the theme with NULL.

In summary, the main differences between theme_set(), theme_update(), and theme_replace() are:

theme_set() completely overrides the current theme.
theme_update() modifies a particular element of the current theme using the + operator.
theme_replace() modifies a particular element of the current theme using the %+replace% operator.

Examples

Run this code

p <- ggplot(mtcars, aes(mpg, wt)) +
  geom_point()
p

# Use theme_set() to completely override the current theme.
# theme_update() and theme_replace() are similar except they
# apply directly to the current/active theme.
# theme_update() modifies a particular element of the current theme.
# Here we have the old theme so we can later restore it.
# Note that the theme is applied when the plot is drawn, not
# when it is created.
old <- theme_set(theme_bw())
p

theme_set(old)
theme_update(panel.grid.minor = element_line(colour = "red"))
p

theme_set(old)
theme_replace(panel.grid.minor = element_line(colour = "red"))
p

theme_set(old)
p


# Modifying theme objects -----------------------------------------
# You can use + and %+replace% to modify a theme object.
# They differ in how they deal with missing arguments in
# the theme elements.

add_el <- theme_grey() +
  theme(text = element_text(family = "Times"))
add_el$text

rep_el <- theme_grey() %+replace%
  theme(text = element_text(family = "Times"))
rep_el$text

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