title: Plotting difference between datasets using ggplot
body: <p>I'm struggling with something I'm trying to do in R. </p>
  
  <p>I have two datasets with the same (categorical) columns but different values. I want to compare the count of each combination of columns (e.g. male and married, female and single etc) visually. 
  This is easy enough to do with ggplot's geom_bar for each dataset, and I know I can put the counts for each dataset next to each other by binding them and setting position = "dodge". </p>
  
  <p>My question is whether there's an easy to way to plot the <em>difference</em> between the two counts for each pair of variables. And whether there's a way of changing the default 'count' method in geom_count (ironic I know) to other things (like proportion or, maybe in this case, a predefined set of values for the difference). </p>
  
  <p>Thanks</p>