title: Map an array of arrays
body: <p>Is there a method in lodash to map over an array of arrays</p>
  
  <p>I would like to do something like this so that it keeps the structure of the array.</p>
  
  <pre><code>def double(x) { return x*2 }
  
  _([[1,2],[3,4]]).somemethod(double) == [[2,4],[6,8]]
  </code></pre>