AngularJS - Ordering a set of results +/- more options, iterating over an object

In the following example, we take advantage of more angular magic. To each string representing the search criteria we will add a '+' or a '-' to indicate the reverse or not direction of our set order.
As we get more advanced on our order criteria, we moved from a simple string to an object holding the key value map.
Example: {'+name': 'Name: A-Z','-name': 'Name: Z-A'}

    <div>
      <h3>Order By:</h3>
      <select data-ng-model='selectedSortOrder2'
           data-ng-options="k as v for (k,v) in {'+name': 'Name: A-Z','-name': 'Name: Z-A', '+lastName': 'Last Name: A-Z', '-lastName': 'Last Name: Z-A ', '+age': 'Age: Young to Experienced', '-age': 'Age: Experienced to Young' }" 
           data-ng-init="selectedSortOrder2='+name'">
      </select>  
   </div>
   <div>
     <h3>List of results:</h3>
     <div ng-repeat="person in results | orderBy:selectedSortOrder2">
       {{person.name}} {{person.lastName}} - {{person.age}}
     </div>
   </div>

Note: In order to iterate over this object, Angular provides us with a dsl expression we can use in the ng-options. In this case it will be 'k as v for (k,v) in optionsSet'. There are other available expressions:

• label for (key , value) in object
• select as label for (key , value) in object
• label group by group for (key, value) in object
• select as label group by group for (key, value) in object

Useful links:

• AngularJS Docs: select

Working Example: Plunkr