title: Underscore: sortBy() based on multiple attributes
body: <p>I am trying to sort an array with objects based on multiple attributes. I.e if the first attribute is the same between two objects a second attribute should be used to comapare the two objects. For example, consider the following array:</p>
  
  <pre><code>var patients = [
               [{name: 'John', roomNumber: 1, bedNumber: 1}],
               [{name: 'Lisa', roomNumber: 1, bedNumber: 2}],
               [{name: 'Chris', roomNumber: 2, bedNumber: 1}],
               [{name: 'Omar', roomNumber: 3, bedNumber: 1}]
                 ];
  </code></pre>
  
  <p>Sorting these by the <code>roomNumber</code> attribute i would use the following code:</p>
  
  <pre><code>var sortedArray = _.sortBy(patients, function(patient) {
      return patient[0].roomNumber;
  });
  </code></pre>
  
  <p>This works fine, but how do i proceed so that 'John' and 'Lisa' will be sorted properly?</p>