title: Max/Min value of Dictionary of List
body: <p>I have a dictionary mapping an id_ to a list of data values like so: <code>dic = {id_ : [v1, v2, v3, v4]}</code>.
  I'm trying to iterate through every value in the dictionary and retrieve the max/min of a certain index of the list mappings.</p>
  
  <p>What I want to do is something like this:</p>
  
  <pre><code>maximum = max([data[0], ??) for id_, data in self.dic.items()])
  </code></pre>
  
  <p>...but obviously this will not work. Is it possible to do this in one line as above?</p>