You have a dataset containing information on US citizens who donated blood in the last year, including addresses and blood types. The O- blood type, also known as "universal donor", is one of the most valuable blood types in the world because it can be transfused to nearly any person. Your goal here is to help a group of researchers find the number of citizens with O- blood type per US state. Unfortunately, the address column comes in a single line, so to extract the state information you will have to perform some data wrangling. They also asked you to create a choropleth map of the US to visualize the results.