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/** | ||
* Groups array items into a Map, given a function to produce grouping key. | ||
*/ | ||
export function groupBy<K, T>( | ||
list: ReadonlyArray<T>, | ||
keyFn: (item: T) => K, | ||
): Map<K, ReadonlyArray<T>> { | ||
const result = new Map<K, Array<T>>(); | ||
for (const item of list) { | ||
const key = keyFn(item); | ||
const group = result.get(key); | ||
if (group === undefined) { | ||
result.set(key, [item]); | ||
} else { | ||
group.push(item); | ||
} | ||
} | ||
return result; | ||
} |
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