title: Exclude or include the particular row from the mat-table view
body: <p>I have a material data table like <code>id</code>  <code>title</code> <code>description</code><br>
  The data source for my <code>mat-table</code> is represented by <code>dataSource$: Observable&lt;Thing[]&gt;</code></p>
  
  <pre><code>&lt;mat-table #table [dataSource]="dataSource$ | async"&gt;
  ...
  &lt;mat-table&gt;
  </code></pre>
  
  <p>Based on a dropdown I want to be able to show all the data(the way it works at the moment) but also to hide the items that have <code>description</code> empty and way around hide the items that have <code>description</code> not empty.</p>
  
  <p>I think I have to do that through the custom pipe? or use a <code>.filter()</code> on my observable?<br>
  Any thoughts how to aproach that best?</p>
  
  <p><strong>UPDATE:</strong></p>
  
  <p>I am trying to use <code>.filter()</code> but got an issue, have no data displayed with that:</p>
  
  <pre><code>dataSource$ = originalDataSource$.filter((item: any) =&gt; item.description == null)
  </code></pre>
  
  <p>thoughts?</p>