25 lines
879 B
JavaScript
25 lines
879 B
JavaScript
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//#region src/math/sumBy.ts
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/**
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* Calculates the sum of an array of numbers when applying
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* the `getValue` function to each element.
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*
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* If the array is empty, this function returns `0`.
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*
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* @template T - The type of elements in the array.
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* @param {readonly T[]} items - An array to calculate the sum.
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* @param {(element: T, index: number) => number} getValue - A function that selects a numeric value from each element.
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* It receives the element and its zero‑based index in the array.
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* @returns {number} The sum of all the numbers as determined by the `getValue` function.
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*
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* @example
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* sumBy([{ a: 1 }, { a: 2 }, { a: 3 }], (x, i) => x.a * i); // Returns: 8
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* sumBy([], () => 1); // Returns: 0
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*/
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function sumBy(items, getValue) {
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let result = 0;
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for (let i = 0; i < items.length; i++) result += getValue(items[i], i);
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return result;
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}
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//#endregion
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export { sumBy };
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