label_value(labels, multi_line = TRUE)label_both(labels, multi_line = TRUE, sep = ": ")label_context(labels, multi_line = TRUE, sep = ": ")label_parsed(labels, multi_line = TRUE)label_bquote(expr)label_wrap_gen(width = 25, multi_line = TRUE)
Labeller functions are in charge of formatting the strip labels of
facet grids and wraps. Most of them accept a multi_line
argument to control whether multiple factors (defined in formulae
such as ~first + second
) should be displayed on a single
line separated with commas, or each on their own line.
label_value()
only displays the value of a factor while
label_both()
displays both the variable name and the factor
value. label_context()
is context-dependent and uses
label_value()
for single factor facetting and
label_both()
when multiple factors are
involved. label_wrap_gen()
uses strwrap()
for line wrapping.
label_parsed()
interprets the labels as plotmath
expressions. label_bquote()
offers a more flexible
way of constructing plotmath expressions. See examples and
bquote()
for details on the syntax of the
argument.
A labeller function accepts a data frame of labels (character
vectors) containing one column for each factor. Multiple factors
occur with formula of the type ~first + second
.
The return value must be a rectangular list where each 'row' characterises a single facet. The list elements can be either character vectors or lists of plotmath expressions. When multiple elements are returned, they get displayed on their own new lines (i.e., each facet gets a multi-line strip of labels).
To illustrate, let's say your labeller returns a list of two character vectors of length 3. This is a rectangular list because all elements have the same length. The first facet will get the first elements of each vector and display each of them on their own line. Then the second facet gets the second elements of each vector, and so on.
For compatibility with labeller()
, each labeller
function must have the labeller
S3 class.
mtcars$cyl2 <- factor(mtcars$cyl, labels = c("alpha", "beta", "gamma")) p <- ggplot(mtcars, aes(wt, mpg)) + geom_point() # Displaying only the values p + facet_grid(. ~ cyl)
p + facet_grid(. ~ cyl, labeller = label_value)
# Displaying both the values and the variables p + facet_grid(. ~ cyl, labeller = label_both)
# Displaying only the values or both the values and variables # depending on whether multiple factors are facetted over p + facet_grid(am ~ vs+cyl, labeller = label_context)
# Interpreting the labels as plotmath expressions p + facet_grid(. ~ cyl2)
p + facet_grid(. ~ cyl2, labeller = label_parsed)
p + facet_wrap(~vs + cyl2, labeller = label_parsed)
# You can also provide a flexible backquoted expression. The labels # must be backquoted and referred to by their names. p <- ggplot(mtcars, aes(wt, mpg)) + geom_point() p + facet_grid(. ~ vs, labeller = label_bquote(alpha ^ .(vs)))
p + facet_grid(. ~ vs, labeller = label_bquote(.(vs) ^ .(vs)))
p + facet_grid(. ~ vs + am, labeller = label_bquote(.(am) ^ .(vs)))
labeller()