I am trying to merge cross-listed courses into one line. I am unsure how to solve this issue in R. I have two datasets and what I call a “crosswalk” (I am not sure that is the correct term). Dataset1 lists courses a college offers, and Dataset2 contains courses offered by other colleges on the same campus. The crosswalk shows courses taught under multiple course numbers. For example, BIOS775 and STAT771 are considered cross-listed because they cover the same material.