title: *ngFor select a secondary option based on an index
body: <p>I have a ngFor with a t. which has a t.product and 4 price options <code>[t.price,t.price1,t,price2,t.price3]</code></p>
  
  <p>This all works great for the first t.price but I cant switch the price from t.price to t.price1 etc based on a radio button selection index 0 to 3. How can I select the t.price based on an index value?</p>
  
  <p>tried to build an another array with only the correct price but that generate errors and does not update the price info at all in the ngFor loop.</p>
  
  <pre><code>&lt;div id="mat-s" &gt;
      &lt;mat-selection-list #list [(ngModel)]="ChkBtnSelection" (ngModelChange)="onNgModelChange($event)"&gt;
        &lt;mat-list-option dense *ngFor="let t of prodT" [value]="t.product" class="mat-list-item"&gt;  
          &lt;div class="div_t"&gt;
            &lt;p class="alignleft"&gt;{{t.product}}&lt;/p&gt;
            &lt;p class="alignright"&gt;  -- {{t.price | currency:'GBP'}}&lt;/p&gt;
          &lt;/div&gt; 
        &lt;/mat-list-option&gt;
      &lt;/mat-selection-list&gt;
  </code></pre>
  
  <p>all works great but I can switch t.price to t.price2? the array has t.price to t.price3.</p>