title: Filtering Observable array elements from another Observable array
body: <p>I had an issue to filter an observable array, in my case it's <code>resources$</code> (an observable which contains all 'resourses' as JSON), and I have another observable called <code>usedResources$</code>, what I want to achieve is simply get <code>unusedResources$</code> from those 2 variables <strong>(resources - usedResources = unusedResources)</strong>, is there any RxJS way to achieve this?</p>