title: How to get the length of piped array in template?
body: <p>sample code:
  if not using pipe, I can get array length by:</p>
  <pre><code>&lt;my-component [arrLen]='arrayA.length'&gt;&lt;/my-component&gt;
  </code></pre>
  <p>But what if I want to get the length of a filtered array by a pipe? (Below not working)</p>
  <pre><code>&lt;my-component [arrLen]='arrayA | arrayFilterPipe:filterParam'&gt;&lt;/my-component&gt;
  </code></pre>
  <p>How to do this? Thanks</p>