Highlight a line in ggplot with multiple lines

Question

I want to change the size, linetype, color etc. for one line in ggplot. Here is a minimal reproducible example:

library         


        

Answer 1

Following this duplicate here is another answer to this question.
It uses a simple trick, to tell the highlighted variable by comparing it with the target value. This dichotomyzes it, becoming a logical FALSE/TRUE value.

variable == "Country1"

The plot legend now needs more care to be taken, in order to have its title and text right.

g <- ggplot(df_long, aes(x = Horizons, y = value)) + 
  geom_line(aes(colour = variable == "Country1", size = variable == "Country1", group = variable)) +
  scale_color_manual(name = "variable", labels = c("Other", "Country1"), values = c("grey50", "red")) +
  scale_size_manual(name = "variable", labels = c("Other", "Country1"), values = c(0.5, 2)) +
  theme_bw()

g