19 lines
511 B
TypeScript
19 lines
511 B
TypeScript
/**
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* https://tc39.es/ecma262/multipage/fundamental-objects.html#sec-object.groupby
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*/
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export function objectGroupBy<T, K extends PropertyKey>(
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items: Iterable<T>,
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keySelector: (item: T, index: number) => K,
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): Partial<Record<K, T[]>> {
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const result = Object.create(null) as Partial<Record<K, T[]>>
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let index = 0
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for (const item of items) {
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const key = keySelector(item, index++)
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if (result[key] === undefined) {
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result[key] = []
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}
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result[key].push(item)
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}
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return result
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}
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