Function group

group<V, K extends Primitive>(
key: (item: NoInfer<V>) => Awaitable<K>,
): Task<V, readonly [K, readonly V[]]>
Creates a task collecting items sharing the same key.

Groups are emitted in first-appearance order of their key, with items inside each group in source order. Keys are limited to Primitive values and compared with SameValueZero semantics, so NaN matches itself and -0 matches 0.
Warning
- Exhaustive: the whole feed is drained before the first group is emitted, so an infinite feed never completes.
- Materialising: the whole feed is held in memory before grouping, so a large feed may exhaust it.
- Stateful: groups cover the items drawn, so a task invoked per nested feed or per run groups each independently, yielding the same key once per invocation rather than once for the feed as a whole.
Type Parameters
- V
  The type of items in the feed
- K extends Primitive
  The type of the grouping key
Parameters
- key: (item: NoInfer<V>) => Awaitable<K>
  The function extracting the grouping key from each item
Returns Task<V, readonly [K, readonly V[]]>
A task yielding each distinct key paired with the read-only list of the items sharing it
Example
```
await pipe(
  (items([1, 2, 3, 4]))
  (group(n => n%2))
  (toArray())
);  // [[1, [1, 3]], [0, [2, 4]]]

await pipe(
  (items([{ id: 1 }, { id: 2 }, { id: 1 }]))
  (group(x => x.id))
  (toArray())
);  // [[1, [{ id: 1 }, { id: 1 }]], [2, [{ id: 2 }]]]
```
- Defined in tasks/group.ts:61