title: Reactive forms: mark dirty all controls in form group
body: <p>I have Angular 6 app with form. Here is an examle</p>
  
  <pre><code>export class ExampleComponent implements OnInit {
      form: FormGroup;
  
      constructor(private fb: FormBuilder) { }
  
      ngOnInit() {
          this.form = new FormGroup({
              first: new FormControl(),
              last: new FormControl()
          });
  
          this.markControlsAsDirty(this.form);
      }
  
      markControlsAsDirty(form: FormGroup) {
          this.form.get('first').markAsDirty();
          this.form.get('last').markAsDirty();
      }
  }
  </code></pre>
  
  <p>I don't want to get a single control and mark every field.
  Can I mark all controls in form group as dirty?</p>
  
  <p><strong>UPDATE</strong> I've been added <a href="https://stackblitz.com/edit/angular-fgek4l" rel="noreferrer">stackblitz example</a> to show that two previous answers were wrong</p>