52 lines
1.3 KiB
TypeScript
52 lines
1.3 KiB
TypeScript
export function countIf<T>(f: (x: T) => boolean, xs: T[]): number {
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return xs.filter(f).length;
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}
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export function count<T>(x: T, xs: T[]): number {
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return countIf(y => x === y, xs);
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}
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export function concat<T>(xss: T[][]): T[] {
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return ([] as T[]).concat(...xss);
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}
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export function intersperse<T>(sep: T, xs: T[]): T[] {
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return concat(xs.map(x => [sep, x])).slice(1);
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}
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export function erase<T>(x: T, xs: T[]): T[] {
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return xs.filter(y => x !== y);
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}
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/**
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* Finds the array of all elements in the first array not contained in the second array.
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* The order of result values are determined by the first array.
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*/
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export function difference<T>(includes: T[], excludes: T[]): T[] {
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return includes.filter(x => !excludes.includes(x));
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}
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export function unique<T>(xs: T[]): T[] {
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return [...new Set(xs)];
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}
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export function sum(xs: number[]): number {
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return xs.reduce((a, b) => a + b, 0);
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}
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export function groupBy<T>(f: (x: T, y: T) => boolean, xs: T[]): T[][] {
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const groups = [] as T[][];
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for (const x of xs) {
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if (groups.length !== 0 && f(groups[groups.length - 1][0], x)) {
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groups[groups.length - 1].push(x);
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} else {
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groups.push([x]);
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}
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}
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return groups;
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}
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export function groupOn<T, S>(f: (x: T) => S, xs: T[]): T[][] {
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return groupBy((a, b) => f(a) === f(b), xs);
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}
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