title: Set default value for mat-select
body: <p>I have a mat-select. when I first show the form I want it to select the first item in the select after the data is loaded. How can I do this?</p>
  <pre><code>  &lt;mat-select 
            placeholder=&quot;period&quot;
            (selectionChange)=&quot;selectperiod($event)&quot;
            (ngModel)=&quot;(periodoptions)&quot;
          &gt;
            &lt;mat-option
              *ngFor=&quot;let p of periodoptions | async&quot;
              [value]=&quot;p.periodid&quot;
            &gt;
              {{ p.periodstart }}
            &lt;/mat-option&gt;
          &lt;/mat-select&gt;
  </code></pre>
  <p>using this to call function to pull rest data</p>
  <pre><code> of(this.getperiods()).subscribe(pp =&gt; {
        this.periodoptions = pp;
  </code></pre>