AngularJS - ng-repeat to assign/generate a new unique ID

You may need something like below when you got a nested ng-repeat:

<label id="country-{{$parent.$index}}-{{$index}}" ng-repeat="city in country.cites"> {{city.name}} </label>

You can use $index https://docs.angularjs.org/api/ng/directive/ngRepeat

<li ng-repeat="country in countries" data-show="????">
    {{country.name}} has population of {{country.population}}

    <div id="country-{{$index}}">
        <p>Expand/collapse content
    </div>
</li>