title: Filtering NSArray of NSDictionary objects
body: <p>filter the array remove duplicates of key value city
  i need to display only city names in first tableview without duplicates and when did select i need to show particular departments in next tableview </p>
  
  <p>example for india i need to show three departments in next view 
  Please suggest me </p>
  
  <pre><code>Array values :(
          {
          city = uk;
          department = "Sales support";
  
      },
          {
  
          city = us;
          department = "Sales support";
  
      },
          {
            city = italy;
            department = "Sales support";
             },
          {
  
          city = india;
          department = "x";
      },
          {
  
          city = india;
          department = "y";
              },
          {
  
          city = india;
          department = "z";
             },
  
     )
  </code></pre>