# Return an array of elements sorted by occurrences
	#
	# ~~~
	# var c = new Counter[String].from(["a", "a", "b", "b", "b", "c"])
	# assert c.sort == ["c", "a", "b"]
	# ~~~
	fun sort: Array[E]
	do
		var res = map.keys.to_a
		var sorter = new CounterComparator[E](self)
		sorter.sort(res)
		return res
	end