title: ngFor filter by text using trackby
body: <p>I'm working on an angular 4 application and I have a big array of objects (like 200 rows)
  So I put a search input and the ngFor is related with a pipe that filters by name according to what you write in the input.
  Something like this</p>
  <pre><code>&lt;input type=&quot;text&quot; [(ngModel)]=&quot;searchtext&quot; placeholder=&quot;Search&quot;&gt;
  &lt;div *ngFor=&quot;let m of (devices | filterEquipments : searchtext)&quot;&gt;{{ m.name }}&lt;/div&gt;
  </code></pre>
  <p>The problem is when I start typing. Apparently filtering is very slow while rendering content in html.
  So, researching a solution, I could see that by using &quot;trackBy&quot; in the &quot;ngFor&quot; it is possible to optimize the result.
  The problem is that I don't know how to implement it correctly and if this can help me filter elements faster.</p>
  <p>How can I implement a fast filter?</p>