Function count

packages/db-ivm/src/operators/count.ts:31–51

()

 * Counts the number of elements by key (version-free)
 */
export function count<
  KType extends T extends KeyValue<infer K, infer _V> ? K : never,
  VType extends T extends KeyValue<KType, infer V> ? V : never,
  T,
>() {
  return (
    stream: IStreamBuilder<T>,
  ): IStreamBuilder<KeyValue<KType, number>> => {
    const output = new StreamBuilder<KeyValue<KType, number>>(
      stream.graph,
      new DifferenceStreamWriter<KeyValue<KType, number>>(),
    )
    const operator = new CountOperator<KType, VType>(
      stream.graph.getNextOperatorId(),
      stream.connectReader() as DifferenceStreamReader<KeyValue<KType, VType>>,
      output.writer,
    )
    stream.graph.addOperator(operator)
    return output
  }
}