Compare two Maps in Scala

Try:

val diff = (m1.keySet -- m2.keySet) ++ (m2.keySet -- m1.keySet)

diff contains the elements that are in m1 and not in m2 and that are in m2 and not in m1.

Consider the difference between the maps converted into sets of tuples,

(m1.toSet diff m2.toSet).toMap