11 lines
264 B
JavaScript
11 lines
264 B
JavaScript
function countBy(map, mapper) {
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const result = new Map();
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for (const [key, value] of map) {
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const mappedKey = mapper(value, key, map);
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result.set(mappedKey, (result.get(mappedKey) ?? 0) + 1);
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}
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return result;
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}
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export { countBy };
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