title: Rxjs operator: filter array of array
body: <p>I have an observable which contains an array of object arrays. For example the pseudocode below</p>
  <pre><code>observable = Observable([[object1, object2], [object3, object4],[object5], [object6]]])
  </code></pre>
  <p>Now, I want to map through the arrays and check if object.name === 'something' and return first occurrence. If no object in a list match, then return undefined. From each array only one object will be returned. So the output will be like <code>Observable([object2, object3, undefined, object6])</code>. How can I do this with rxjs operator?</p>