35 lines
1.3 KiB
JavaScript
35 lines
1.3 KiB
JavaScript
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//#region src/set/countBy.ts
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/**
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* Counts the occurrences of items in a Set based on a transformation function.
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*
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* This function takes a Set and a function that generates a key from each value.
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* It returns a Map with the generated keys and their counts as values.
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* The count is incremented for each element for which the transformation produces the same key.
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*
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* @template T - The type of elements in the Set.
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* @template K - The type of keys produced by the transformation function.
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* @param {Set<T>} set - The Set to count occurrences from.
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* @param {(value: T, value2: T, set: Set<T>) => K} mapper - The function to produce a key for counting.
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* @returns {Map<K, number>} A Map containing the mapped keys and their counts.
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*
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* @example
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* const set = new Set([1, 2, 3, 4, 5]);
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* const result = countBy(set, (value) => value % 2 === 0 ? 'even' : 'odd');
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* // result will be Map(2) { 'odd' => 3, 'even' => 2 }
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*
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* @example
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* const set = new Set(['apple', 'banana', 'cherry']);
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* const result = countBy(set, (value) => value.length);
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* // result will be Map(2) { 5 => 1, 6 => 2 }
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*/
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function countBy(set, mapper) {
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const result = /* @__PURE__ */ new Map();
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for (const value of set) {
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const mappedKey = mapper(value, value, set);
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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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//#endregion
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exports.countBy = countBy;
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