title: How do I write a value doubling iterator?
body: <p>I want to start with a base value of <code>1</code> and then multiply my base value by <code>2</code> each iteration up to a defined limit (say the total length of my array).</p>
  
  <p>Do I have to implement a special iterator just to do this? Or can I combine other iterator methods like <code>map</code> and <code>filter</code> together  in order to achieve the same functionality. Though I would imagine implementing my iterator specifically would be more efficient, but also more verbose.</p>