title: How to keep the stream after a forkJoin or a concatAll(), toArray()
body: <p>I am trying, for the sake of learning, to keep the stream after, for instance, a forkjoin. But I would like to do it with pipe (in an elegant way). Not just recover the array, and then rewrite a from(array).subscribe, again.</p>
  
  <p>I tried to do a from, inside the pipe, but that doesn't work. Also I would like to know (as bonus questions) what would be the ideal way, in the pipe (first pipe in this case, because I suposse there will be 2 pipes), to modify each mock_post call result BEFORE the array of the forkJoin is returned. </p>
  
  <p>Just a little mock function that I created to simulate a dummy api return value after 2s.</p>
  
  <pre><code>    private mock_post(url: string): Observable&lt;object&gt; {
          return from(timer(2000)).pipe(
              map(result =&gt; {
                  return {id: 2, name: 'mock', source: url};
              })
          );
      }
  
  </code></pre>
  
  <p>First test case with ForkJoin (using above function)</p>
  
  <pre><code>
  
          const operations = [];
          operations.push(this.mock_post('/api/test/'));
          operations.push(this.mock_post('/api/test/2'));
          operations.push(this.mock_post('/api/test/3'));
  
          forkJoin(operations).pipe(
  
          )
              .subscribe(
                  (next) =&gt; {
                      console.log(next);
                  }
              );
  
  </code></pre>
  
  <p>Second test case with concatAll() + toArray().</p>
  
  <pre><code>    const obs: Observable&lt;any&gt; = from(operations);
          obs.pipe(
              map(result =&gt; {
                  // I want to modify the result here, and add something to the object or modify a property (for example)
                  console.log(`result-&gt; `, result); // This is(obviously, returning an observable, but how do I get the final value here?)
  
                  result.name = 'mock_modified';
  
                  return result;
              }),
              concatAll(),
              toArray()
          ).subscribe(
              (next) =&gt; {
                  console.log(`-&gt; NEXT`, next);
              },
              (error) =&gt; {
                  console.log(`* ERROR`, error);
              },
              () =&gt; {
                  console.log('=) COMPLETE');
              }
          );
  </code></pre>
  
  <p>If anyone can shed some ligth here, it would be great. I hope I explained  myself correctly.</p>