scala> val a = Set(1, 2, 3)
a: scala.collection.immutable.Set[Int] = Set(1, 2, 3)

scala> a map (x => Set(x, a diff Set(x)))
res: scala.collection.immutable.Set[scala.collection.immutable.Set[Any]] = Set(Set(1, Set(2, 3)), Set(2, Set(1, 3)), Set(3, Set(1, 2)))

或者

scala> for (x <- a) yield Set(x, a diff Set(x))
res: scala.collection.immutable.Set[scala.collection.immutable.Set[Any]] = Set(Set(1, Set(2, 3)), Set(2, Set(1, 3)), Set(3, Set(1, 2)))