I am working on a research paper that is concerned with money flows between countries. I have project-level data for each country pairing so in some years there may be multiple or zero projects and thus money flows. For example, in 2006 Austria committed to four projects in Burundi, but in 2007, there were only three and five in 2008. I want to show the total money flows for each country pair for each year, so that I can merge this dataset with another country-level dataset. Does anyone know how I can aggregate this project-level data to just get the totals?