Take an array of stations (with marketCity as an attribute) and create an array of marketCities (with stations as an attribute)

SortStations.js

// Define the unique market cities
$scope.marketCities = [];
for (var i = 0; i < data.query.results.station.length; i++){
  // if it isn't already there, add it
  if(i !== 0 && data.query.results.station[i].marketCity !== data.query.results.station[i-1].marketCity){
    $scope.marketCities.push({ label: data.query.results.station[i].marketCity, stations: [data.query.results.station[i]]});
  }else if(i == 0){
    $scope.marketCities.push({ label: data.query.results.station[i].marketCity, stations: [data.query.results.station[i]]});
  }else if(data.query.results.station[i].id !== data.query.results.station[i-1].id){
    // is the market already there? well, just add the station then.
    $scope.marketCities[$scope.marketCities.length-1].stations.push(data.query.results.station[i]);
  }
}