How to do it...

1. Wrap the add_axis() function with several arguments declared to work as a title function:

> library(ggvis)
> ggvis_title <- function(vis, plot_title, title_size = 18, shift = 0, ...){ 
    add_axis(vis, 'x', ticks = 0, orient = 'top', 
             properties = axis_props( axis = list(strokeWidth = 0),
                                      labels = list(strokeWidth = 0), 
                                      grid = list(strokeWidth = 0),
                                      title = list(fontSize = title_size, dy = -shift, ...)),
             title = plot_title)
  }

1. Try it on the previous plot:

> sca3 %>% ggvis_title('simple ggvis scatterplot')

The result looks like the following image:

Figure 2.2 - titled ggvis scatterplot.

Now to the explanations.