get rows of unique values by group

Question

I have a data.table and want to pick those lines of the data.table where some values of a variable x are unique relative to another variable y

It\'s possible to get

Answer 1

The idiomatic data.table way is:

require(data.table)
unique(dt, by = c("y", "x"))
#    y x z
# 1: a 1 1
# 2: a 2 2
# 3: b 3 4
# 4: b 2 5
# 5: b 1 6