title: Change FormBuilder array items in nested forms
body: <p>According to the API documentation the proper way to change nested values is to use method <code>patchValue</code> </p>
  
  <p><code>myForm.patchValue({'key': {'subKey': 'newValue'}});</code></p>
  
  <p>But how to change values in nested arrays like <strong>list</strong> of cars in this example below. How to get first item of <strong>list</strong> array an change <code>model</code> to <code>Fiesta</code>? <a href="http://plnkr.co/edit/K6VB3O?p=preview" rel="nofollow noreferrer">Plunker</a></p>
  
  <p><code>myForm.patchValue({'list': 0: {'model': 'Fiesta'});</code> is not working.</p>
  
  <pre><code>@Component({
    moduleId: __moduleName,
    selector: 'my-app',
    template: `&lt;div&gt;&lt;pre&gt;{{ myForm.value | json }}&lt;/pre&gt;&lt;/div&gt;`
  })
  export class AppComponent {
  
    public myForm: FormGroup;
  
    constructor(@Inject(FormBuilder) private _fb: FormBuilder) {
  
      this.myForm = this._fb.group({
        name: 'Cars',
        list:  this._fb.array([
          this.initCar(),
          this.initCar(),
          this.initCar()
        ]),
      });
      /** Change value Here **/
      this.myForm.patchValue({name: 'Automobile'});
    };
  
    initCar() {
      return this._fb.group({
        automaker: 'Ford',
        model:     'Fusion'
      });
    }
  }
  </code></pre>
  
  <p><a href="http://plnkr.co/edit/K6VB3O?p=preview" rel="nofollow noreferrer">Plunker</a></p>