title: Search element in nsdictionary by value
body: <p>I have nsdictionary which contains elements with following structure</p>
  
  <p>name --> value</p>
  
  <p>email--> key</p>
  
  <p>I get value(of above structure) from user,
  now I want to search element in nsdictionary by value(entered by user) not by key, whether it is present in nsdictionary or not and also want to get index of that element if present.</p>
  
  <p>How to do this?</p>