Add dynamic subtitle using ggplot

Question

I am trying to use ggplot to add a subtitle. Similar question was asked here: How to add a ggplot2 subtitle with different size and colour?, and the answer was as follows:<

Answer 1

You should use function bquote() instead of expression() to use titles that are stored as variables. And variable names should be placed inside .()

plot.title = 'TITLE'
plot.subtitle = 'SUBTITLE'

ggplot(mtcars,aes(disp,mpg))+geom_point()+
  ggtitle(bquote(atop(.(plot.title), atop(italic(.(plot.subtitle)), "")))) 

UPDATE - ggplot2 version 2.2.1

The latest ggplot2 version now can produce subtitles directly, so you don't have to use bquote() and expression(). The result is atchieved with argument subtitle = of function labs().

ggplot(mtcars,aes(disp,mpg))+geom_point()+
      labs(title = plot.title,subtitle = plot.subtitle) +
      theme(plot.subtitle = element_text(face = "italic"))