​

const players = {

   player_1: {

     name: 'a',

     carsKeys: {

         car_id_1: true,

         car_id_2: true,

         car_id_3: true

     }

   },

   player_2: {

     name: 'b'

   }

};

​

const cars = {

  car_id_1: {

      property_1: '111',

      property_2: '11',

   },

  car_id_2: {

    property_1 : '222',

    property_2 : '22'

  },

  car_id_3: {

    property_1 : '333',

    property_2 : '33'

  }

}

​

const players$ = Rx.Observable.of(players)

  .map(x => players[Object.keys(x).find(x=> x === 'player_1')])

  .map(x => Object.keys(x.carsKeys))

  .switchMap(x => Rx.Observable.from(x))

  .map(x => cars[x])

  ;

​

let result = []

players$.subscribe(x => {

  result.push(x);

  console.log(result)

})

​

​