My analyses are computationally intensive, so I whittle down the data frame as much as I can. For one, I drop columns I don’t need.
BBS$countrynum <- NULL
It’s also convenient that routes are associated with regions in the routes.csv file. So, once I merge that data, I can choose to keep only routes in certain Bird Conservation Regions (BCR).
BBS <- BBS[BBS$BCR %in% c(), ]
By looking through the supplementary info, you’ll find much useful info that can be used to subset the data.