$scope.formatDate = function(date) {
    return '42';
  };

  $scope.columns = [
    {field: 'date', cellTemplate: '<div class="ui-grid-cell-contents">formatDate({{row.entity.date}})</div>'},
    {field: 'title'},
    {field: 'quantity'},
    //[...]
  ];

$scope.columns = [
    {field: 'getFormattedDate()'},
    //[...]
  ];

  $http.post('/api/data/').success(function (data) {
    $scope.gridOptions.data = data.elements;

    $scope.gridOptions.data.forEach(function(row) {
      row.getFormattedDate = function() {
        return '42';
      }
    })
  });

{
    name: 'date',
    cellTemplate: '<div class="ui-grid-cell-contents">{{grid.appScope.parseDate(row.entity.date)}}</div>'
}

<div class="ui-grid-cell-contents">{{ formatDate(row.entity.date) }}</div>

columnDefs: [
            {
                name: 'starRating', headerCellClass: 'blue', headerTooltip: 'Star Rating',
                cellTemplate: '{{grid.appScope.formatRating(row.entity.starRating)}}'
            },

columnDefs: [
            {
                name: 'starRating', headerCellClass: 'blue', headerTooltip: 'Star Rating',
                cellTemplate: '<span>{{grid.appScope.formatRating(row.entity.starRating)}}</span>'
            },

$scope.formatRating = function (starRating) {
        switch (starRating) {
            case "ONE": return "1/5"; break;
            case "TWO": return "2/5"; break;
            case "THREE": return "3/5"; break;
            case "FOUR": return "4/5"; break;
            case "FIVE": return "5/5"; break;
        }
    }