title: Use Lodash map to reorganize list into sorted keys by value
body: <p>I am can't figure out how to do this without iterating over the array three times.</p>
  
  <p>I am looking to transform an array of job listings that look like this:</p>
  
  <pre><code>const jobs = [
    {
      title: 'Manager',
      department: 'Retail',
      location: 'New York'
    },
    {
      title: 'Customer Service Rep',
      department: 'Corporate',
      location: 'Washington D.C.'
    },
    {
      title: 'Clerk',
      department: 'Retail',
      location: 'New York'
    },
    ...
  ];
  </code></pre>
  
  <p>Into an object of <em>unique</em> departments with associated jobs:</p>
  
  <pre><code>const deps = {
    'Corporate': [
      {
        title: 'Customer Service Rep',
        department: 'Corporate',
        location: 'Washington D.C.'
      },
    ],
    'Retail': [
      {
        title: 'Manager',
        department: 'Retail',
        location: 'New York'
      },
      {
        title: 'Clerk',
        department: 'Retail',
        location: 'New York'
      },
    ],
  };
  </code></pre>
  
  <p>Is <code>_map</code> my best bet here? Is there a more eloquent way of doing this?</p>