Function group

group<Iter, T>(iter, key?): AnyItResult<Iter, Map<T, AnyItV<Iter>[]>>
Groups the passed-in iterable by the given key.
Type Parameters
- Iter extends AnyIt<unknown>
- T = AnyItV<Iter>
Parameters
- iter: Iter
  A sync or async iterable.
- Optional key: ValFunc<AnyItV<Iter>, T>
  A function computing the key, such as item => item['foo']. Key defaults to an identity function, grouping duplicated values.
Returns AnyItResult<Iter, Map<T, AnyItV<Iter>[]>>
A Map where each key is a group.
Example
```
// Returns Map(1: [1, 1], 2: [2, 2], 3: [3])
it.group([1, 1, 2, 2, 3])
```
Example
```
// Returns Map(true: [1, 1], false: [2, 2, 3])
it.group([1, 1, 2, 2, 3], x => x < 2)
```
Example
```
// Returns Map(1: [{id: 1}], 2: [{id: 2}])
it.group([{id: 1}, {id: 2}], x => x.id)
```
- Defined in src/operators/group.ts:35