Comment by hadley
4 years ago
From dbplyr experience, folks want to be able to do stuff like `across(which(is.numeric), mean)`, which you can't do currently because dplyr doesn't know the column types (although it does maintain a list of the column names).
Yes, that's a good example.
Indeed — often SQL doesn't know the column _names_, let alone the types. So for cross-column selection (e.g. `across`), this does become necessary.