93 lines
2.4 KiB
TypeScript
93 lines
2.4 KiB
TypeScript
/**
|
|
* Returns the sum of all the elements of a numeric array.
|
|
* @param arr Numeric array.
|
|
*/
|
|
export function sumArray(arr: ReadonlyArray<number>): number {
|
|
return sumBy(arr, (a) => a);
|
|
}
|
|
|
|
/**
|
|
* Returns the sum of all the elements of any array,
|
|
* given a lamda function to receive the numeric representation of each element.
|
|
* @param arr Any array.
|
|
* @param by Map element to number or string, which will be interpreted as a number.
|
|
*/
|
|
export function sumBy<E>(
|
|
arr: ReadonlyArray<E>,
|
|
by: (element: E) => number | string
|
|
): number {
|
|
return arr.reduce((sum, element) => sum + Number(by(element)), 0);
|
|
}
|
|
|
|
/**
|
|
* Returns the product of a numeric array.
|
|
* @param arr Numeric array.
|
|
*/
|
|
export function multArray(arr: ReadonlyArray<number>): number {
|
|
return multBy(arr, (a) => a);
|
|
}
|
|
|
|
/**
|
|
* Returns the product of any array,
|
|
* given a lamda function to receive the numeric representation of each element.
|
|
* @param arr Any array.
|
|
* @param by Map element to number or string, which will be interpreted as a number.
|
|
*/
|
|
export function multBy<E>(
|
|
arr: ReadonlyArray<E>,
|
|
by: (element: E) => number | string
|
|
): number {
|
|
if (arr.length <= 0) {
|
|
return 0;
|
|
}
|
|
return arr.reduce((sum, element) => sum * Number(by(element)), 1);
|
|
}
|
|
|
|
/**
|
|
* Group an array by a given key.
|
|
* @param arr Any array.
|
|
* @param by Map element to key.
|
|
* @param equals Check if two keys are identical. Defaults to strict equality.
|
|
*/
|
|
export function groupBy<E, K>(
|
|
arr: ReadonlyArray<E>,
|
|
by: (element: E) => K,
|
|
equals: (a: K, b: K) => boolean = (a, b) => a === b
|
|
): { key: K; elements: Array<E> }[] {
|
|
return arr.reduce(
|
|
(groups, element) => {
|
|
const key = by(element);
|
|
const index = groups.findIndex((e) => equals(e.key, key));
|
|
|
|
if (index < 0) {
|
|
// New key found, add to group array.
|
|
groups.push({ key, elements: [element] });
|
|
return groups;
|
|
}
|
|
|
|
const existing = groups[index];
|
|
existing.elements.push(element);
|
|
|
|
return groups;
|
|
},
|
|
[] as { key: K; elements: Array<E> }[]
|
|
);
|
|
}
|
|
|
|
/**
|
|
* Return the middle Element of an array, rounding up.
|
|
* Returns undefined for empty arrays without throwing!
|
|
*
|
|
* @example
|
|
* ```typescript
|
|
* getMiddleElement([1, 2, 3, 4]) === 3
|
|
* getMiddleElement([1, 2, 3]) === 2
|
|
* getMiddleElement([1]) === 1
|
|
* getMiddleElement([]) === undefined
|
|
* ```
|
|
* @param arr
|
|
*/
|
|
export function getMiddleElement<E>(arr: ReadonlyArray<E>) {
|
|
return arr[Math.floor(arr.length / 2)];
|
|
}
|