title: How to quickly retrieve only a subset of a Set in Redis
body: <p>I have need to store an unordered set of items in a manner that allows for fast </p>
  
  <ul>
  <li>Insert</li>
  <li>Membership testing (and/or intersection)</li>
  <li>Random subset retrieval</li>
  </ul>
  
  <p>Redis seems like a great candidate for this kind of storage, but as I read the docs, there's not one data type that fits this perfectly. Having a SUBSET command for the Set type would be perfect.</p>
  
  <p>What's the best way to store and query this kind of data structure?</p>