import { PickByValue } from '@johngw/stream-common/Object';
import { Stringable } from '@johngw/stream-common/String';
/**
 * Accumulates each chunk into an object where the key is the result of
 * calling a provided function or using a chunk's property.
 *
 * The key can be the result of a property on the chunk.
 *
 * @group Transformers
 * @see {@link label:function}
 * @example
 * ```
 * --one------------two------------------three-----------------------------
 *
 * groupBy('length')
 *
 * --{'3':['one']}--{'3',['one','two']}--{'3':['one','two'],'5':['three']}-
 * ```
 */
export declare function groupBy<T, K extends keyof PickByValue<T, Stringable>>(propName: K): TransformStream<T, Record<string, T[]>>;
/**
 * The key can be the result of calling a provided function.
 *
 * @example
 * ```
 * --6.1----------4.2--------------------6.3------------------------
 *
 * groupBy(Math.floor)
 *
 * --{'6':[6.1]}--{'4':[4.2],'6':[6.1]}--{'4':[4.2],'6':[6.1,6.3]}--
 * ```
 */
export declare function groupBy<T, G extends Stringable>(propName: (chunk: T) => G): TransformStream<T, Record<string, T[]>>;