How to make ng-repeat filter out duplicate results

Or you can write your own filter using lodash.

app.filter('unique', function() {
    return function (arr, field) {
        return _.uniq(arr, function(a) { return a[field]; });
    };
});

You could use the unique filter from AngularUI (source code available here: AngularUI unique filter) and use it directly in the ng-options (or ng-repeat).

<select ng-model="orderProp" ng-options="place.category for place in places | unique:'category'">
    <option value="0">Default</option>
    // unique options from the categories
</select>