title: Convert Observable<any> to Observable<customtype> in angular2, typescript
body: <p>How can we convert between types in typescript? like Observable <code>&lt;any&gt;</code> to Observable<code>&lt;array of custom_type&gt;</code>.
  Do we need to use map function to map each value in incoming item of list or is there some other typecasting mechanism?</p>
  
  <p>sample code</p>
  
  <pre><code>private list: Observable&lt;any&gt;;
  this.list = af.database.list('/list/') //af: AngularFire
  </code></pre>