/
reduce_groups.ts
36 lines (34 loc) · 1.13 KB
/
reduce_groups.ts
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// Copyright 2018-2024 the Deno authors. All rights reserved. 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.
*
* @template T input type of an item in a group in the given grouping.
* @template A type of the accumulator value, which will match the returned record's values.
* @example
* ```ts
* import { reduceGroups } from "https://deno.land/std@$STD_VERSION/collections/reduce_groups.ts";
* import { assertEquals } from "https://deno.land/std@$STD_VERSION/assert/assert_equals.ts";
*
* const votes = {
* "Woody": [2, 3, 1, 4],
* "Buzz": [5, 9],
* };
*
* const totalVotes = reduceGroups(votes, (sum, it) => sum + it, 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, (it) => it.reduce(reducer, initialValue));
}