Code for Calculating Contiguous Events for the States

This is code that I use to automatically calculate the count and percentage of contiguous states that have experienced an event in the past. This is most commonly used for studies of inter-state policy diffusion, however it can be applied to any previous event (e.g., court decisions) in neighboring states that is expected to affect the likelihood of current state action. I also include mock adoption data for state anti-bullying and stand your ground laws. This allows the user to better understand how the code will work for their own event data. I include code for a dataset of a single event and one for multiple different types of events (e.g., a large adoption dataset like that used in Boehmke and Skinner 2012). I certainly appreciate comments on improving this code and eliminating any errors.