tail()
returns the last 6 items of a subsettable object. When using aggregate()
, the parameters to the FUN
argument are passed immediately after the function using a comma; here 1
refers to n = 1
, which tells tail()
to only return the last item.
aggregate(a[, c('NUM', 'VAL')], list(a$ID), tail, 1)
# Group.1 NUM VAL
# 1 A 2 0
# 2 B 3 0
# 3 C 9 0