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| 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 | 1x 1x 1x 4x 4x | import { Mapper } from "@benneq/function";
import { reduce } from "./reduce";
/**
* Creates a {@link Function} that groups all elements of an {@link Iterable}
* by using a {@link Mapper} function and returns a {@link Map} containing the
* grouped values for each mapped key.
*
* @example
* ```ts
* const groupByEvenOdd = groupBy(isEven);
* const result = groupByEvenOdd([1,2,1,3]);
* console.log(result); // Map([[1, [1,1,3]], [0, [2]]])
* ```
*
* @typeParam T - the {@link Iterable} value type
* @typeParam K - the {@link Map} key type
* @param mapper - the key {@link Mapper} function
* @returns a {@link Map} containing the grouped values
*/
export const groupBy = <T, K>(
mapper: Mapper<T, K>
): ((iterable: Iterable<T>) => Map<K, T[]>) => {
return reduce(
(acc, value, key = mapper(value), values = acc.get(key) ?? []) => {
values.push(value);
return acc.set(key, values);
},
new Map<K, T[]>()
);
};
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