// Copyright 2018-2025 the Deno authors. MIT license.
// This module is browser compatible.
import { mapValues } from "./map_values.ts";
/**
* Applies the given reducer to each group in the given grouping, returning the
* results together with the respective group keys.
*
* @typeParam T input type of an item in a group in the given grouping.
* @typeParam A type of the accumulator value, which will match the returned
* record's values.
*
* @param record The grouping to reduce.
* @param reducer The reducer function to apply to each group.
* @param initialValue The initial value of the accumulator.
*
* @returns A record with the same keys as the input grouping, where each value
* is the result of applying the reducer to the respective group.
*
* @example Basic usage
* ```ts
* import { reduceGroups } from "@std/collections/reduce-groups";
* import { assertEquals } from "@std/assert";
*
* const votes = {
* Woody: [2, 3, 1, 4],
* Buzz: [5, 9],
* };
*
* const totalVotes = reduceGroups(votes, (sum, vote) => sum + vote, 0);
*
* assertEquals(totalVotes, {
* Woody: 10,
* Buzz: 14,
* });
* ```
*/
export function reduceGroups<T, A>(
record: Readonly<Record<string, ReadonlyArray<T>>>,
reducer: (accumulator: A, current: T) => A,
initialValue: A,
): Record<string, A> {
return mapValues(record, (value) => value.reduce(reducer, initialValue));
}
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