export type Mapper<Input, Output> = (input: Input) => Output;
export type GroupByMergeFunction<V> = (a: V, b: V) => V;
declare global {
    interface Array<T> {
        /**
         * Perform a group by operation grouping by the result of the keyMapper.
         * @param keyMapper used to get the key
         * @param valueMapper used to get the value
         * @param mergeFunction unify two items into a unique items with the same key
         * @returns a map with the elements grouped by the keys generated using the keyMapper
         */
        groupBy<K, V>(keyMapper: Mapper<T, K>, valueMapper: Mapper<T, V>, mergeFunction?: GroupByMergeFunction<V>): Map<K, V>;
        /**
         * Perform a group by operation grouping by the result of the keyMapper.
         * @param keyMapper used to get the key
         * @param valueMapper used to get the value
         * @param mergeFunction unify two items into a unique items with the same key
         * @returns an object with the elements grouped by the keys generated using the keyMapper
         */
        groupByToDictionary<K extends string, V>(keyMapper: Mapper<T, K>, valueMapper: Mapper<T, V>, mergeFunction?: GroupByMergeFunction<V>): Record<K, V>;
        /**
         * Perform a group by operation grouping by the result of the keyMapper.
         * As the simplified version of a groupby this method only allows to
         * group by objects by specific keys generating an array of elements
         * for each key.
         * @param keyMapper used to get the key
         * @returns a map with the elements grouped by the keys generated using the keyMapper
         */
        simpleGroupBy<K>(keyMapper: Mapper<T, K>): Map<K, T[]>;
        /**
         * Perform a group by operation grouping by the result of the keyMapper.
         * As the simplified version of a groupby this method only allows to
         * group by objects by specific keys generating an array of elements
         * for each key.
         * @param keyMapper used to get the key
         * @returns a map with the elements grouped by the keys generated using the keyMapper
         */
        simpleGroupByToDictionary<K extends string>(keyMapper: Mapper<T, K>): Record<K, T[]>;
    }
}