Counting string variables

[Bailey Henderson]

Year	City	Year	Events
2018	London	2018	2
2018	London	2017	2
2017	London
2017	London

Hey Im new to stata and was hoping to get some help with something. I am trying to plot a graph of events against year, where essentially the events is a combination of occurrences that occurred within a specific year. Would someone please advise me on how to do this, please?

I am basically trying to turn the first 2 columns into the last 2 columns in bold.

[Rich Goldstein]

help contract

[Bailey Henderson]

help contract

I'll look into this, thank you for your response!