title: How to get and set value in nested form fields in angular2?
body: <p>I am working on angular2 application and using angular reactive forms.
  How to get value of innermost element and set its value.</p>
  
  <pre><code>form : FormGroup;
  
  constructor(private formBuilder: FormBuilder)
  {
     this.form = formBuilder.group({
        'home_cleaning' : [{
             cities : FormBuilder.array([])
         }]
     });
  }
  
  setValue()
  {
      let cities_array = [1,2,3,4];
      this.form.controls['home_cleaning']['cities'].setValue(cities_array);
  }
  
  getValue()
  {
     console.log(this.form.controls['home_cleaning']['cities'].value);
  }
  </code></pre>
  
  <p>Getting error in console : Cannot read property 'setValue/value'  of undefined.</p>