aggregate
fun <K, inV, outV> KGroupedStream<K, inV>.aggregate( initializer: Initializer<outV>, materialized: Materialized<K, outV, KeyValueStore<Bytes, ByteArray>>, aggregator: Aggregator<K, inV, outV>): KTable<K, outV>
fun <K, inV, outV> KGroupedStream<K, inV>.aggregate( name: String, materialized: Materialized<K, outV, KeyValueStore<Bytes, ByteArray>>, initializer: Initializer<outV>, aggregator: Aggregator<K, inV, outV>): KTable<K, outV>