title: Is there a unique filter in angular 2?
body: <p>I have a json as follows:</p>
  
  <pre><code>[{
    "_id": "58a58ea23744cd46918914ef",
    "entityId": "ce7200c1-3430-47ce-ab81-7d0622cb8cae",
    "name": "Portugal",
    "description": "Portugal",
    "type": "country",
    "category": "common",
    "subcategory": "common",
    "parent": {
      "_id": "58a8486ca4890027348a8966"
    },
    "image": {
      "_id": "58a8486ca4890027348a8965"
    },
    "metadata": {
      "primary": "pt",
      "taxRate": 20,
      "exchangeRate": 0.7,
      "language": "PT",
      "currency": "EUR",
      "_id": "58a8486ca4890027348a8964"
    }
  }, {
    "_id": "58a58ea23744cd46918914f1",
    "entityId": "815b9e90-e36f-4488-ad50-6a259b6d034d",
    "name": "Qatar",
    "description": "Qatar",
    "type": "country",
    "category": "common",
    "subcategory": "common",
    "parent": {
      "_id": "58a8486ca4890027348a8969"
    },
    "image": {
      "_id": "58a8486ca4890027348a8968"
    },
    "metadata": {
      "primary": "qa",
      "taxRate": 20,
      "exchangeRate": 0.7,
      "language": "RO",
      "currency": "RO",
      "_id": "58a8486ca4890027348a8967"
    }
  }, {
    "_id": "58a58ea23744cd46918914f2",
    "entityId": "e12ea227-c05c-42cf-b746-6bc537812a02",
    "name": "Romania",
    "description": "Romania",
    "type": "country",
    "category": "common",
    "subcategory": "common",
    "parent": {
      "_id": "58a8486ca4890027348a896c"
    },
    "image": {
      "_id": "58a8486ca4890027348a896b"
    },
    "metadata": {
      "primary": "ro",
      "taxRate": 20,
      "exchangeRate": 0.7,
      "language": "RO",
      "currency": "RON",
      "_id": "58a8486ca4890027348a896a"
    }
  }, {
    "_id": "58a58ea23744cd46918914f4",
    "entityId": "8c22ccaf-f7b7-4009-9642-54580ad5ad4e",
    "name": "Russia",
    "description": "Russia",
    "type": "country",
    "category": "common",
    "subcategory": "common",
    "parent": {
      "_id": "58a8486ca4890027348a8972"
    },
    "image": {
      "_id": "58a8486ca4890027348a8971"
    },
    "metadata": {
      "primary": "ru",
      "taxRate": 20,
      "exchangeRate": 0.7,
      "language": "RU",
      "currency": "RUB",
      "_id": "58a8486ca4890027348a8970"
    }
  }, {
    "_id": "58a58ea23744cd46918914fa",
    "entityId": "725b2011-177b-4fc5-8e1f-559b3e4e8958",
    "name": "United States",
    "description": "United States",
    "type": "country",
    "category": "common",
    "subcategory": "common",
    "parent": {
      "_id": "58a8486ca4890027348a8984"
    },
    "image": {
      "_id": "58a8486ca4890027348a8983"
    },
    "metadata": {
      "primary": "us",
      "taxRate": 20,
      "exchangeRate": 0.7,
      "language": "EN",
      "currency": "USD",
      "_id": "58 a8486ca4890027348a8982"
    }
  }, {
    "_id": " 58 a58ea23744cd46918914d8",
    "entityId": "af884be9 - 067 d - 4 dd2 - 8646 - 5738 f5bb0efb",
    "name": "Germany",
    "description": "Germany",
    "type": "country",
    "category": "common",
    "subcategory": "common",
    "parent": {
      "_id": "58 a8486ca4890027348a89b7 "
    },
    "image": {
      "_id": "58 a8486ca4890027348a89b6 "
    },
    "metadata": {
      "primary": "de",
      "taxRate": 20,
      "exchangeRate": 0.7,
      "language": "DE",
      "currency": "EUR",
      "_id": "58 a8486ca4890027348a89b5 "
    }
  }]
  </code></pre>
  
  <p>And I'm displaying these values in dropdown with the following code:</p>
  
  <p><strong>Template:</strong></p>
  
  <pre><code>&lt;div class="dropdown"&gt;
    &lt;button class="btn btn-default dropdown-toggle" type="button" id="dropdownMenu1" data-toggle="dropdown" aria-haspopup="true"&gt;
      {{selectedCurrency}}
      &lt;span class="caret"&gt;&lt;/span&gt;
    &lt;/button&gt;
    &lt;ul class="dropdown-menu" aria-labelledby="dropdownMenu1"&gt;
      &lt;li *ngFor="let currency of currencies"&gt;
        &lt;a&gt;{{currency.metadata.currency }}&lt;/a&gt;
      &lt;/li&gt;
    &lt;/ul&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p>Right now if you see, metadata has duplicate currency <strong><code>"EUR"</code></strong> . Is there a pipe with angular2 so that I can display only the unique values of <code>metadata.currency</code></p>