21 lines
No EOL
891 B
TypeScript
21 lines
No EOL
891 B
TypeScript
//#region src/fp/array/countBy.d.ts
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/**
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* Creates a function that counts values by a derived key.
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*
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* The mapper receives each value, its index, and the full input array. The returned object
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* uses mapper results as keys and occurrence counts as values.
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*
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* @template T - The type of elements in the array.
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* @template K - The property-key type produced by the mapper.
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* @param mapper - Called with each value, index, and array to produce a key.
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* @returns A function that maps a readonly array to counts by key.
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*
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* @example
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* import { countBy, pipe } from 'es-toolkit/fp';
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*
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* pipe([1, 2, 3, 4, 5], countBy(value => (value % 2 === 0 ? 'even' : 'odd')));
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* // => { odd: 3, even: 2 }
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*/
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declare function countBy<T, K extends PropertyKey>(mapper: (item: T, index: number, array: readonly T[]) => K): (array: readonly T[]) => Record<K, number>;
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//#endregion
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export { countBy }; |