-
Notifications
You must be signed in to change notification settings - Fork 577
/
aggregate_groups.ts
52 lines (50 loc) · 1.53 KB
/
aggregate_groups.ts
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
// Copyright 2018-2023 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
*
* @example
* ```ts
* import { aggregateGroups } from "https://deno.land/std@$STD_VERSION/collections/aggregate_groups.ts";
* import { assertEquals } from "https://deno.land/std@$STD_VERSION/testing/asserts.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, Array<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,
],
);
}