fun <A, K> <ERROR CLASS><A>.recordAsAssociation(toKey: (A) -> K, merge: (K, A, A) -> A = { _key, _oldValue, newValue -> newValue }): ObservableMap<K, out A>This variant simply associates each event with its key.
toKey - Function retrieving the key to associate with.merge - The function to be called if there is an existing element at the key.