Add partition function

[aleclarson]

Inspired by the Deno stdlib: https://github.com/denoland/std/blob/e8e47da19e2393da4f58b93d7d8377b83698c6f4/collections/partition.ts#L1

import { partition } from "@std/collections/partition";
import { assertEquals } from "@std/assert";

const numbers = [5, 6, 7, 8, 9];
const [even, odd] = partition(numbers, (it) => it % 2 === 0);

assertEquals(even, [6, 8]);
assertEquals(odd, [5, 7, 9]);

Nice thing about this, versus Radashi's group(), is two fold:

• Guarantees arrays to exist even if one or both are empty (though it's limited to exactly 2 arrays)
• More readable due to predicate function, instead of mapping values to “group IDs”

This would make partition a nice addition.

Concerns

1. Is having both group and partition too confusing?
2. Is partition not a clear enough name?

Feel free to voice your opinions below. ✌️

[Minhir]

Radashi example with group:

import { group } from "radashi";

const numbers = [5, 6, 7, 8, 9];
const { even = [], odd = [] } = group(numbers, (it) =>
  it % 2 === 0 ? "even" : "odd",
);

It also guarantees arrays to exist even if one or both are empty. Maybe not as readable as partition but more extendable. You can make it "Fizz", "Buzz", and "FizzBuzz". I prefer to have one option. It may be worth to put this code as an example.

[aleclarson]

Agreed on all you've said!

I wonder if we could add a special case for boolean results, treating it as a predicate rather than a “group name” factory. Maybe it's complicating things too much? But it feels like a nice compromise.

const [even, odd] = group(numbers, it => it % 2 === 0)

We already limit the group callback to string | number | symbol, so adding boolean would be additive, not breaking.