title: angular material 2 button toggle by default selected
body: <p>in angular material 2, How can I set default selected button in toggle group.</p>
  
  <p>It does toggle once I tap one, but both selected by default somehow.
  I tried as follows, but doesn't work.</p>
  
  <pre><code>  &lt;md-button-toggle-group #group="mdButtonToggleGroup"&gt;
      &lt;md-button-toggle (click)="firstTapped()" selected&gt;
        &lt;span&gt;one&lt;/span&gt;
      &lt;/md-button-toggle&gt;
      &lt;md-button-toggle (click)="secondTapped()"&gt;
        &lt;span&gt;second&lt;/span&gt;
      &lt;/md-button-toggle&gt;
    &lt;/md-button-toggle-group&gt;
  </code></pre>