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reduce_groups.ts
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reduce_groups.ts
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// Copyright 2018-2022 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
*
* ```ts
* import { reduceGroups } from "https://deno.land/std@$STD_VERSION/collections/mod.ts"
* import { assertEquals } from "https://deno.land/std@$STD_VERSION/testing/asserts.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, Array<T>>>,
reducer: (accumulator: A, current: T) => A,
initialValue: A,
): Record<string, A> {
return mapValues(record, (it) => it.reduce(reducer, initialValue));
}