title: Mapping a range in ruby
body: <p>Is there a simple way of mapping a range to another kind of range in ruby without iterating over the whole range? 
  Basically what I'm trying to achieve is this</p>
  
  <pre><code>## mapping this
  range = 1..5
  ## into this
  date_range = (1.year.ago)..(5.years.ago)
  </code></pre>
  
  <p>The best I came up with was this:</p>
  
  <pre><code>(range.begin.years.ago)..(range.end.years.ago)
  </code></pre>
  
  <p>Is there a method that would let me do something like:</p>
  
  <pre><code>range.map {|e| e.years.ago} 
  </code></pre>