I want to create a variable which counts the total number of people on a company board per year. The difficulty is that the number changes every year. I have 20 dummy variables for every year, equaling to 1 if the person is present on board, and 0 if not present. I also have a variable id, with a unique number for every company. I can see the total board members per company when I tab id y2020. How can I create this into a variable, which counts the total number of board members, per company, for each year hence calculating Board Size?