title: map vs subscribe in @ngrx/store
body: <p>I am new to angular2, currently, I am working on a project which using @ngrx/store and subscribe classes. I am confused on map method is not working while subscribe store is working. Please help me in understanding when to use map and subscribe method. The code is below.</p>
  
  <pre><code>this.store.select('rating').subscribe(({ topPicks }) =&gt; { // code is working });
  this.store.select('rating').map(({ topPicks }) =&gt; // not working);
  </code></pre>