TypeScript partition array into two by condition, performance compare

test.ts

import { Bench } from "tinybench";

const bench = new Bench({
	time: 1000,
});

// This will not change the origin array
function partition<T>(
	arr: readonly T[],
	predicate: (item: T) => boolean,
): [T[], T[]] {
	return arr.reduce(
		(acc, item) => {
			acc[predicate(item) ? 0 : 1].push(item);
			return acc;
		},
		[[], []] as [T[], T[]],
	);
}

// This will consume the origin array
function partitionInPlace<T>(
	array: T[],
	predicate: (item: T) => boolean,
): [T[], T[]] {
	const match: T[] = [];
	const nonMatch: T[] = [];
	while (array.length > 0) {
		const item = array.pop() as T;
		if (predicate(item)) {
			match.push(item);
		} else {
			nonMatch.push(item);
		}
	}
	return [match, nonMatch];
}

const a = Array.from({ length: 10000 }, (_, i) => i);

bench
	.add("partition by reduce", () => {
		const [match, nonMatch] = partition(a, (i) => i % 2 === 0);
	})
	.add("partition by pop", () => {
		const [match, nonMatch] = partitionInPlace(a, (i) => i % 2 === 0);
	});

await bench.run();
console.table(bench.table());

// Output:
// ┌───────┬───────────────────────┬───────────┬────────────────────┬──────────┬─────────┐
// │ (idx) │ Task Name             │ ops/sec   │ Average Time (ns)  │ Margin   │ Samples │
// ├───────┼───────────────────────┼───────────┼────────────────────┼──────────┼─────────┤
// │     0 │ "partition by reduce" │ "17,601"  │ 56813.90182933754  │ "±0.83%" │ 17602   │
// │     1 │ "partition by pop"    │ "737,664" │ 1355.6304013341596 │ "±0.48%" │ 737665  │
// └───────┴───────────────────────┴───────────┴────────────────────┴──────────┴─────────┘

If each element in Array a is Object, the performance difference will be bigger.

┌───────┬───────────────────────┬───────────┬────────────────────┬──────────┬─────────┐
│ (idx) │ Task Name             │ ops/sec   │ Average Time (ns)  │ Margin   │ Samples │
├───────┼───────────────────────┼───────────┼────────────────────┼──────────┼─────────┤
│     0 │ "partition by reduce" │ "8,015"   │ 124755.72604790462 │ "±0.68%" │ 8016    │
│     1 │ "partition by pop"    │ "756,371" │ 1322.1010004322566 │ "±0.41%" │ 756373  │
└───────┴───────────────────────┴───────────┴────────────────────┴──────────┴─────────┘