title: Undefined errors generated by rxjs switchmap used with filter (Angular 2 + ngrx/store + redux)
body: <p>I'm working in an Angular 2.3 app using ngrx/store + the redux pattern.</p>
  
  <p>In pulling a list of objects from my store (i.e. big image at the top of pages), I'm getting an undefined error that I'm trying to troubleshoot. It looks like it might be a race condition where the function is resolving prior to the observable. In any case, I'm still getting the result but trying to understand the error:</p>
  
  <pre><code>error_handler.js:50 EXCEPTION: Cannot read property 'filter' of undefined
  TypeError: Cannot read property 'filter' of undefined
  </code></pre>
  
  <p>I have in the constructor (which has <code>private _store: Store</code>)</p>
  
  <pre><code>objects$: Observable&lt;Object[]&gt; = _store.select(s =&gt; s.objects)
  </code></pre>
  
  <p>and my function is:</p>
  
  <pre><code>selectObject(id: number): Observable&lt;Object&gt; {
      return this.objects$
        .switchMap( objects =&gt; objects.filter( object =&gt; object.id === id));
  }
  </code></pre>