title: check if there are two or more equal values in Json
body: <p>How I should process this Json, to extract the <strong>cat1</strong> value once in a Spinner, and in the second Spinner based on the first spinner selection I display <strong>book1</strong> and <strong>book2</strong>.</p>
  
  <p><strong>Json:</strong></p>
  
  <pre><code>{
   "library":
  [
  {
     "Cat": "cat1",
     "Book": "book1",
     "authur": "authur1"
   },
   {
     "Cat": "cat1",
     "Book": "book2",
     "authur": "authur2"
   },
   {
     "Cat": "cat2",
     "Book": "book3",
     "authur": "authur3"
   }
  ]
  }
  </code></pre>