# filterMapValues

Filter and map values.

## Signatures

```ts
export declare const filterMapValues: {
    <K, V, B>(f: (value: V, key: K) => Option.Option<B>): <E, R>(ref: RefHashMap<K, V, E, R>) => RefSubject.Computed<HashMap.HashMap<K, B>, E, R>;
    <K, V, E, R, B>(ref: RefHashMap<K, V, E, R>, f: (value: V, key: K) => Option.Option<B>): RefSubject.Computed<HashMap.HashMap<K, B>, E, R>;
};
```

## Why

Projects hash map state with filter map values for both current reads and future pushes,
avoiding a second mutable cache of the derived value.

## Ownership and lifetime

The filter map values view retains no independent state. An Effect read samples the source once;
Fx observation follows later pushes and its observing Scope owns subscription cleanup.