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

Not every line but you can plot only 'Country1' separately :

library(ggplot2)

ggplot(subset(df_long, variable != 'Country1'), aes(x = Horizons, y = value)) + 
  geom_line(aes(colour = variable, group = variable)) +
  geom_line(data = subset(df_long, variable == 'Country1'), 
            size = 3, linetype = 'dashed', color = 'blue') +
  theme_bw()