title: Angular map. What is it?
body: <p>I am learning Angular 6 and I am puzzled with constructions like a:</p>
  
  <pre><code>this.contentArray.map((v: string, i: number) =&gt; `Content line ${i + 1}`)
  </code></pre>
  
  <p>or like a:</p>
  
  <pre><code>return this.aService.getItems()
      .pipe(map(response =&gt; response.data));
  </code></pre>
  
  <p>I am run through the couples of book like a "The_Complete_Book_on_Angular_6" or "Pro Angular 6" (Adam Freeman) but there are no simple explanations there. Google kept silence about that too. <strong>Can someone give the right and good tutorial or may be book (for amateurs) about <em>array.map, array.filter</em> and about <em>.pipe(map(...))?</em></strong></p>