# Construct a partitioning on `es`, a subset of elements
	#
	#     var s = new DisjointSet[Int]
	#     s.add_all([1,2,3,4,5,6])
	#     s.union(1,2)
	#     s.union(1,3)
	#     s.union(4,5)
	#     var p = s.to_subpartition([1,2,4])
	#     assert p.length == 2
	fun to_subpartition(es: Collection[E]): Collection[Set[E]]
	do
		var map = new HashMap[DisjointSetNode, Set[E]]
		for e in es do
			var ne = find(e)
			var set = map.get_or_null(ne)
			if set == null then
				set = new HashSet[E]
				map[ne] = set
			end
			set.add(e)
		end
		return map.values
	end