title: How can I loop through nested json and get array unique value from field
body: <p>I got this format in json.
  I need unique values of "volume". So in result I'd get only '30' and '40'.
  I used loop inside of another loop, but it returns unique values from each product, which is not what I want.
  I'm using Angular 1 in Ionic.</p>
  
  <pre><code>{
  
  "data": [
      {
          "id": 1,
          "title": "Category title",
          "products": [
              {
                  "id": 1,
                  "title": "product title",
                  "volume": "40"
              },
              {
                  "id": 2,
                  "title": "product title",
                  "volume": "30"
              }
          ]
      },
  
      {
          "id": 2,
          "title": "Another Category title",
          "products": [
              {
                  "id": 3,
                  "title": "product title",
                  "volume": "40"
              },
              {
                  "id": 3,
                  "title": "product title",
                  "volume": "30"
              }
          ]
      }
  
  ]
  
  }
  </code></pre>
  
  <p>Thanks</p>