Two columns x-axis in ggplot2 (point first, point second)

I have quarterly data as follows (the key represents a quarter of a quarter):

       tic    saleq    key
1     AAPL 1346.202 1990-2
2     AAPL 1364.760 1990-3
3     NOK  1354.090 1990-4

      

        
        
        
      

    

Since it is now in one column, I can plot the line with the combined column as the x-axis:

p <- ggplot(example, aes(x = key, y = saleq))
p + geom_line(aes(color=tic, group=tic)) + ylab("Quarterly sales")

      

        
        
        
      

    

However, this (logically) generates many duplicate "year" values ​​(i.e. column x is littered 2014-1, 2014-2)

I would like to be able to plot this with ggplot2, "grouping" by year, and then displaying the quarter just above it on the x-axis. Similar to plotting a line graph in Excel, as with this data. Is this possible in ggplot2?

I was redirected to this question which is trying something similar. However, this leaves out naming multiple "groups" of x-values: should I dynamically calculate where the midpoint of each year is (to account for the number of data quarters per year?)