chunkByPredicate

1/**
2 * Splits an array into chunks whenever the predicate returns true.
3 * The chunk boundary is placed before the element where the predicate succeeds.
4 * The predicate is applied to each element (excluding the first).
5 *
6 * @param arr - The array to split.
7 * @param predicate - A function that determines if a new chunk should start.
8 * @returns An array of chunked arrays.
9 */
10export function chunkByPredicate<T>(
11  arr: T[],
12  predicate: (current: T, index: number, array: T[]) => boolean
13): T[][] {
14  if (!arr.length) return [];
15
16  const result: T[][] = [];
17  let currentChunk: T[] = [arr[0]];
18
19  for (let i = 1; i < arr.length; i++) {
20    if (predicate(arr[i], i, arr)) {
21      result.push(currentChunk);
22      currentChunk = [arr[i]];
23    } else {
24      currentChunk.push(arr[i]);
25    }
26  }
27
28  result.push(currentChunk);
29  return result;
30}

1test('chunkByPredicate - chunks on even numbers', () => {
2  const input = [1, 3, 5, 2, 7, 2, 4];
3  const output = chunkByPredicate(input, x => x % 2 === 0);
4  expect(output).toEqual([[1, 3, 5], [2, 7], [2], [4]]);
5});
6
7test('chunkByPredicate - splits on negative numbers', () => {
8  const input = [10, 20, -1, 30, -2, 40];
9  const output = chunkByPredicate(input, x => x < 0);
10  expect(output).toEqual([[10, 20], [-1, 30], [-2, 40]]);
11});
12
13test('chunkByPredicate - empty array', () => {
14  expect(chunkByPredicate([], () => true)).toEqual([]);
15});
16
17test('chunkByPredicate - no predicate match', () => {
18  expect(chunkByPredicate([1, 2, 3], () => false)).toEqual([[1, 2, 3]]);
19});
20
21test('chunkByPredicate - predicate always true', () => {
22  expect(chunkByPredicate([1, 2, 3], () => true)).toEqual([[1], [2], [3]]);
23});