title: Angular 6: How to use an array in template syntax with ngFor?
body: <p>I have two arrays: <strong>books</strong> and <strong>booksDisplay</strong>. In my template I use <code>*ngFor</code> to iterate through my <code>booksDisplay</code> array:</p>
  
  <pre><code>&lt;div *ngFor="let bookDisplay of booksDisplay"&gt;
     &lt;div class="book"&gt;
        &lt;div class="title" *ngIf="???"&gt;{{ ???.title }}
     &lt;/div&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p>But inside my <code>*ngFor</code>-Element I need to look up in my <code>books</code>-Array, where <code>id</code> is equal to the current <code>bookId</code> in my <code>booksDisplay</code>-Array. So how can I use something like a where clause inside my <code>*ngFor</code>-Element?</p>