Counting distinct by category

Hi

I have this following set of data:

My aim is to create a bar chart to list the count of distinct key, by category.

The complication comes in because for every unique key with different categories, it shld fall into just 1 category. Do determine which category it falls under (based on the lowest check_code for every unique key). So I should get something like this:

Eventually I hope to get a bar chart with this breakdown:

Appreciate if someone could assist please, thanks!