ですです。こんなのも

 public init<S: Sequence>( _ keysAndValues: S, uniquingKeysWith combine: (Value, Value) throws -> Value ) rethrows where S.Iterator.Element == (Key, Value) {

 public init<S: Sequence>( grouping values: S, by keyForValue: (S.Iterator.Element) throws -> Key ) rethrows where Value == [S.Iterator.Element] {

(edited)