Function topK

packages/db-ivm/src/operators/topK.ts:21–45

(
  comparator: (a: V1Type, b: V1Type) => number,
  options?: TopKOptions,
)

 * @returns A piped operator that limits the number of results
 */
export function topK<
  KType extends T extends KeyValue<infer K, infer _V> ? K : never,
  V1Type extends T extends KeyValue<KType, infer V> ? V : never,
  T,
>(
  comparator: (a: V1Type, b: V1Type) => number,
  options?: TopKOptions,
): PipedOperator<T, T> {
  const limit = options?.limit ?? Infinity
  const offset = options?.offset ?? 0

  return (stream: IStreamBuilder<T>): IStreamBuilder<T> => {
    const reduced = stream.pipe(
      reduce((values) => {
        // `values` is a list of tuples, first element is the value, second is the multiplicity
        const consolidated = new MultiSet(values).consolidate()
        const sortedValues = consolidated
          .getInner()
          .sort((a, b) => comparator(a[0] as V1Type, b[0] as V1Type))
        return sortedValues.slice(offset, offset + limit)
      }),
    )
    return reduced as IStreamBuilder<T>
  }
}

/**
 * Limits the number of results based on a comparator, with optional offset.