title: How do I create an observable of an array from an array of observables?
body: <p>I have an array of <code>Thing</code> objects that I want to convert to <code>ConvertedThing</code> objects, using an asynchronous function that returns <code>Observable&lt;ConvertedThing&gt;</code>.</p>
  
  <p>I'd like to create an <code>Observable&lt;[ConvertedThing]&gt;</code> that emits one value when all the conversions have completed.</p>
  
  <p>How can this be accomplished?  Any help much appreciated!</p>