Function mapOfSimpleMutable

mapOfSimpleMutable<V>(
groupBy?: (value: V) => string,
valueEq?: IsEqual<V>,
): IMapOfMutable<V>
A simple mutable map of arrays, without events. It can store multiple values under the same key.

For a fancier approaches, consider ofArrayMutable, ofCircularMutable or ofSetMutable.
Type Parameters
- V
  Type of items
Parameters
- groupBy: (value: V) => string = defaultKeyer
- valueEq: IsEqual<V> = ...
Returns IMapOfMutable<V>
New instance
Example
```
const m = mapOfSimpleMutable();
m.add(`hello`, 1, 2, 3); // Adds numbers under key `hello`
m.delete(`hello`);       // Deletes everything under `hello`

const hellos = m.get(`hello`); // Get list of items under `hello`
```