Is there a unique filter in angular 2?

Question

I have a json as follows:

[{
  "_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 "
  }
}]

And I'm displaying these values in dropdown with the following code:

Template:

<div class="dropdown">
  <button class="btn btn-default dropdown-toggle" type="button" id="dropdownMenu1" data-toggle="dropdown" aria-haspopup="true">
    {{selectedCurrency}}
    <span class="caret"></span>
  </button>
  <ul class="dropdown-menu" aria-labelledby="dropdownMenu1">
    <li *ngFor="let currency of currencies">
      <a>{{currency.metadata.currency }}</a>
    </li>
  </ul>
</div>

Right now if you see, metadata has duplicate currency "EUR" . Is there a pipe with angular2 so that I can display only the unique values of metadata.currency

Solution

Is there a unique filter in angular 2?

No, you would have to create your custom pipe to do this.

However, I don't think create a pipe is really necessary, you can do it in your component.

You can get all the unique currencies of those items doing the following:

export class AnyComponent {

  items: any[];
  currencies: string[];

  constructor() {
    // Populate your items... "items = blabla"

    // Get all currencies
    const curr = items.map(data => data.metadata.currency);

    // Unique currencies
    this.currencies = curr.filter((x, i, a) => x && a.indexOf(x) === i);
  }
}

Then, in your template:

...
<ul class="dropdown-menu" aria-labelledby="dropdownMenu1">
  <li *ngFor="let currency of currencies">
    <a>{{currency}}</a>
  </li>
</ul>