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std/collections/aggregate_groups.ts

The Deno Standard Library
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// Copyright 2018-2024 the Deno authors. All rights reserved. MIT license.// This module is browser compatible.
import { mapEntries } from "./map_entries.ts";
/** * Applies the given aggregator 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 { aggregateGroups } from "https://deno.land/std@$STD_VERSION/collections/aggregate_groups.ts"; * import { assertEquals } from "https://deno.land/std@$STD_VERSION/assert/assert_equals.ts"; * * const foodProperties = { * "Curry": ["spicy", "vegan"], * "Omelette": ["creamy", "vegetarian"], * }; * const descriptions = aggregateGroups( * foodProperties, * (current, key, first, acc) => { * if (first) { * return `${key} is ${current}`; * } * * return `${acc} and ${current}`; * }, * ); * * assertEquals(descriptions, { * "Curry": "Curry is spicy and vegan", * "Omelette": "Omelette is creamy and vegetarian", * }); * ``` */export function aggregateGroups<T, A>( record: Readonly<Record<string, ReadonlyArray<T>>>, aggregator: (current: T, key: string, first: boolean, accumulator?: A) => A,): Record<string, A> { return mapEntries( record, ([key, values]) => [ key, // Need the type assertions here because the reduce type does not support the type transition we need values.reduce( (accumulator, current, currentIndex) => aggregator(current, key, currentIndex === 0, accumulator), undefined as A | undefined, ) as A, ], );}