Function group

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

The whole feed is drained before the first group is emitted, then 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

Accumulates the whole feed in memory before grouping. For large or infinite feeds, this may exhaust memory or never complete.
Type Parameters
- V
  The type of items in the feed
- K extends Primitive
  The type of the grouping key
Parameters
- key: (item: V) => Awaitable<K>
  The function extracting the grouping key from each item
Returns Task<V, readonly [K, readonly V[]]>
A task pairing each distinct key 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:57