change ggplot legend title with common aesthetics

Question

This happens a lot to draw a ggplot with multiple aesthetic all referring to one variable. Then, to change the common legend title, the simple way I know is to do it for all common aesthetics using labs() or guides().

For example

ggplot(data = mtcars, aes(x = mpg, y = wt, 
                          color = factor(am), shape= factor(am), linetype=factor(am), fill=factor(am))) + 
    geom_point() + geom_smooth() +
    labs(color="long legend title", shape="long legend title", linetype="long legend title", fill="long legend title")

is there any way not to repeat "long legend title" for all common aesthetics in the code?

Answer 1

You could create a list of guide_legends and splice it with !!! to use it in the guides() function:

This might work for you:

library(ggplot2)
library(purrr)

aesthetics <- c("colour", "shape", "linetype", "fill")
# Guides provided to `guides()` must be named.
names(aesthetics) <- aesthetics
guide_legends <- map(aesthetics, ~ guide_legend("long legend title"))

ggplot(data = mtcars, 
       aes(x = mpg, y = wt, 
           color = factor(am), 
           shape= factor(am), 
           linetype=factor(am), 
           fill=factor(am))) +
  geom_point() + 
  geom_smooth() +
  guides(!!!guide_legends)