R's duplicated returns a vector showing whether each element of a vector or data frame is a duplicate of an element with a smaller subscript. So if rows 3, 4, and 5 of a 5-row data frame are the same, duplicated will give me the vector

FALSE, FALSE, FALSE, TRUE, TRUE

But in this case, I actually want to get

FALSE, FALSE, TRUE, TRUE, TRUE

that is, I want to know whether a row is duplicated by a row with a larger subscript too.