forked from FoundKeyGang/FoundKey
139 lines
3.3 KiB
TypeScript
139 lines
3.3 KiB
TypeScript
import { EndoRelation, Predicate } from './relation.js';
|
|
|
|
/**
|
|
* Count the number of elements that satisfy the predicate
|
|
*/
|
|
|
|
export function countIf<T>(f: Predicate<T>, xs: T[]): number {
|
|
return xs.filter(f).length;
|
|
}
|
|
|
|
/**
|
|
* Count the number of elements that is equal to the element
|
|
*/
|
|
export function count<T>(a: T, xs: T[]): number {
|
|
return countIf(x => x === a, xs);
|
|
}
|
|
|
|
/**
|
|
* Concatenate an array of arrays
|
|
*/
|
|
export function concat<T>(xss: T[][]): T[] {
|
|
return ([] as T[]).concat(...xss);
|
|
}
|
|
|
|
/**
|
|
* Intersperse the element between the elements of the array
|
|
* @param sep The element to be interspersed
|
|
*/
|
|
export function intersperse<T>(sep: T, xs: T[]): T[] {
|
|
return concat(xs.map(x => [sep, x])).slice(1);
|
|
}
|
|
|
|
/**
|
|
* Returns the array of elements that is not equal to the element
|
|
*/
|
|
export function erase<T>(a: T, xs: T[]): T[] {
|
|
return xs.filter(x => x !== a);
|
|
}
|
|
|
|
/**
|
|
* Finds the array of all elements in the first array not contained in the second array.
|
|
* The order of result values are determined by the first array.
|
|
*/
|
|
export function difference<T>(xs: T[], ys: T[]): T[] {
|
|
return xs.filter(x => !ys.includes(x));
|
|
}
|
|
|
|
/**
|
|
* Remove all but the first element from every group of equivalent elements
|
|
*/
|
|
export function unique<T>(xs: T[]): T[] {
|
|
return [...new Set(xs)];
|
|
}
|
|
|
|
export function sum(xs: number[]): number {
|
|
return xs.reduce((a, b) => a + b, 0);
|
|
}
|
|
|
|
export function maximum(xs: number[]): number {
|
|
return Math.max(...xs);
|
|
}
|
|
|
|
/**
|
|
* Splits an array based on the equivalence relation.
|
|
* The concatenation of the result is equal to the argument.
|
|
*/
|
|
export function groupBy<T>(f: EndoRelation<T>, xs: T[]): T[][] {
|
|
const groups = [] as T[][];
|
|
for (const x of xs) {
|
|
if (groups.length !== 0 && f(groups[groups.length - 1][0], x)) {
|
|
groups[groups.length - 1].push(x);
|
|
} else {
|
|
groups.push([x]);
|
|
}
|
|
}
|
|
return groups;
|
|
}
|
|
|
|
/**
|
|
* Splits an array based on the equivalence relation induced by the function.
|
|
* The concatenation of the result is equal to the argument.
|
|
*/
|
|
export function groupOn<T, S>(f: (x: T) => S, xs: T[]): T[][] {
|
|
return groupBy((a, b) => f(a) === f(b), xs);
|
|
}
|
|
|
|
export function groupByX<T>(collections: T[], keySelector: (x: T) => string): Record<string, T[]> {
|
|
return collections.reduce((obj: Record<string, T[]>, item: T) => {
|
|
const key = keySelector(item);
|
|
if (!Object.prototype.hasOwnProperty.call(obj, key)) {
|
|
obj[key] = [];
|
|
}
|
|
|
|
obj[key].push(item);
|
|
|
|
return obj;
|
|
}, {});
|
|
}
|
|
|
|
/**
|
|
* Compare two arrays by lexicographical order
|
|
*/
|
|
export function lessThan(xs: number[], ys: number[]): boolean {
|
|
for (let i = 0; i < Math.min(xs.length, ys.length); i++) {
|
|
if (xs[i] < ys[i]) return true;
|
|
if (xs[i] > ys[i]) return false;
|
|
}
|
|
return xs.length < ys.length;
|
|
}
|
|
|
|
/**
|
|
* Returns the longest prefix of elements that satisfy the predicate
|
|
*/
|
|
export function takeWhile<T>(f: Predicate<T>, xs: T[]): T[] {
|
|
const ys = [];
|
|
for (const x of xs) {
|
|
if (f(x)) {
|
|
ys.push(x);
|
|
} else {
|
|
break;
|
|
}
|
|
}
|
|
return ys;
|
|
}
|
|
|
|
export function cumulativeSum(xs: number[]): number[] {
|
|
const ys = Array.from(xs); // deep copy
|
|
for (let i = 1; i < ys.length; i++) ys[i] += ys[i - 1];
|
|
return ys;
|
|
}
|
|
|
|
export function toArray<T>(x: T | T[] | undefined): T[] {
|
|
return Array.isArray(x) ? x : x != null ? [x] : [];
|
|
}
|
|
|
|
export function toSingle<T>(x: T | T[] | undefined): T | undefined {
|
|
return Array.isArray(x) ? x[0] : x;
|
|
}
|