76 lines
2.0 KiB
TypeScript
76 lines
2.0 KiB
TypeScript
/**
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* Returns the sum of all the elements of a numeric array.
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* @param arr Numeric array.
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*/
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export function sumArray(arr: ReadonlyArray<number>): number {
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return sumBy(arr, (a) => a);
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}
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/**
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* Returns the sum of all the elements of any array,
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* given a lamda function to receive the numeric representation of each element.
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* @param arr Any array.
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* @param by Map element to number or string, which will be interpreted as a number.
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*/
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export function sumBy<E>(
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arr: ReadonlyArray<E>,
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by: (element: E) => number | string
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): number {
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return arr.reduce((sum, element) => sum + Number(by(element)), 0);
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}
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/**
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* Returns the product of a numeric array.
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* @param arr Numeric array.
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*/
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export function multArray(arr: ReadonlyArray<number>): number {
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return multBy(arr, (a) => a);
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}
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/**
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* Returns the product of any array,
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* given a lamda function to receive the numeric representation of each element.
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* @param arr Any array.
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* @param by Map element to number or string, which will be interpreted as a number.
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*/
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export function multBy<E>(
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arr: ReadonlyArray<E>,
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by: (element: E) => number | string
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): number {
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if (arr.length <= 0) {
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return 0;
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}
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return arr.reduce((sum, element) => sum * Number(by(element)), 1);
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}
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/**
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* Group an array by a given key.
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* @param arr Any array.
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* @param by Map element to key.
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* @param equals Check if two keys are identical. Defaults to strict equality.
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*/
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export function groupBy<E, K>(
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arr: ReadonlyArray<E>,
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by: (element: E) => K,
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equals: (a: K, b: K) => boolean = (a, b) => a === b
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): { key: K; elements: Array<E> }[] {
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return arr.reduce(
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(groups, element) => {
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const key = by(element);
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const index = groups.findIndex((e) => equals(e.key, key));
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if (index < 0) {
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// New key found, add to group array.
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groups.push({ key, elements: [element] });
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return groups;
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}
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const existing = groups[index];
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existing.elements.push(element);
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return groups;
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},
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[] as { key: K; elements: Array<E> }[]
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);
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}
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