27 lines
633 B
TypeScript
27 lines
633 B
TypeScript
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// Copyright 2021 Signal Messenger, LLC
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// SPDX-License-Identifier: AGPL-3.0-only
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import { reduce } from './iterables';
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/**
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* Like Lodash's `groupBy`, but returns a `Map`.
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*/
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export const groupBy = <T, ResultT>(
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iterable: Iterable<T>,
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fn: (value: T) => ResultT
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): Map<ResultT, Array<T>> =>
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reduce(
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iterable,
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(result: Map<ResultT, Array<T>>, value: T) => {
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const key = fn(value);
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const existingGroup = result.get(key);
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if (existingGroup) {
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existingGroup.push(value);
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} else {
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result.set(key, [value]);
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}
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return result;
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},
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new Map<ResultT, Array<T>>()
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);
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