stores.component.t

storeList$: Observable<Map<string,number>>;
stores$: Observable<string[]>;

ngOnInit() {
    this.stores$ = this.itemsQuery.selectAll().pipe(map(entities =>
      entities.map(entity => entity.store)
      // .filter((elem, index, self) => {
      //   return index === self.indexOf(elem);
      // })
      ));

  this.storeList$ = this.stores$.pipe(map((stores) => this.countItemsPerStore(stores)));
}