title: Angular 6 clicked radio button doesn't update ngModel
body: <p>I have a radio group: </p>
  
  <pre><code>&lt;div class="btn-group"&gt;
    &lt;div class="btn btn-outline-secondary"
    *ngFor="let category of categories"&gt;
      &lt;input
      type="radio"
      [value]="category.id"
      [(ngModel)]="categoryModel.name"&gt;
       {{category.name}}
    &lt;/div&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p>ts</p>
  
  <pre><code>import { Component, ViewEncapsulation } from '@angular/core';
  
  @Component({
    selector: 'test',
    templateUrl: './test.component.html',
    styleUrls: ['./test.component.scss'],
  
  })
  
  export class Test {
  
    categories: {};
    categoryModel = {name: ''};
  
    constructor(private modalService: NgbModal) {
      this.categories = [{
        id: 1, name: 'test1',
      },
      {
        id: 2, name:  'test2'
      },
      {
        id: 3, name:  'test3',
      },
    ]
  }
  </code></pre>
  
  <p>When I click my radio, my model doesn't update, 
        {{categoryModel.name}} 
  is still empty, what is wrong with it, how can I change this?</p>