title: can I pass observable as function parameter?
body: <p>Can I pass observable to function as a parameter ?
  I have two observables that get data from backend and I need to filter them out by a lot of conditions.
  To do not repeat myself I thought about function that will filter observable data and return already filtered one. There will be couple of combineLatest inside as I will be reacting to action streams (values selected on UI).
  I came up with something like:</p>
  <pre><code>    const data1$ = this.service.getData('first');
      const data2$ = this.service.getData('second');
  
      filterData(input$: Observable&lt;string&gt;) : Observable&lt;string&gt; {
  
          const filtered$ = combineLatest(input$, this.service.selectedFiltersData$).pipe(...filtering...taping and so on...)
          const filteredBySomethingElse$(filtered$, this.service.anotherSelectedFilters.pipe(...filtering...taping and so on...)
  
        return filteredBySomethingElse$;
      }
  
      const filtered1$ = this.filterData(data1$);
      const filtered2$ = this.filterData(data2$);
      
  </code></pre>
  <p>Example is extremely simplified :)<br />
  Is that a good practice ?</p>