  We tackle the problem of partitioning players into groups of fixed size, such
as allocating eligible students to shared dormitory rooms. Each student submits
preferences over the other individual students. We study several settings,
which differ in the size of the rooms to be filled, the orderedness or
completeness of the preferences, and the way of calculating the value of a
coalition---based on the best or worst roommate in the coalition. In all cases,
we determine the complexity of deciding the existence, and then finding a
Pareto optimal assignment, and the complexity of verifying Pareto optimality
for a given assignment.
