The natural counterpart to "first of each group" is "last of each group" — the last visit per subject, the latest lab per test, the oldest age in each Sex.
In SAS, once a dataset is sorted by the grouping variable, the automatic flag last.var is TRUE on the last row of each group.
Tidyverse uses group_by() + slice(n()) or slice_tail() to keep the last row within each group.
Base R uses !duplicated(group, fromLast = TRUE) after sorting to keep the last occurrence per group.
This lesson picks the subject with the highest Height within each Sex on CLASS — the mirror image of lesson 2200.
As always, "last" is defined by the sort order, so we sort first and then take the last row.