12 lines
263 B
JavaScript
12 lines
263 B
JavaScript
function countBy(arr, mapper) {
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const result = {};
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for (let i = 0; i < arr.length; i++) {
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const item = arr[i];
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const key = mapper(item, i, arr);
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result[key] = (result[key] ?? 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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