Ng-grid and sorting array data

Question

I'm using ng-grid where the data source is an array of arrays like so

 $scope.myData = [
      ["Moroni", "M"],
      ["Tiancum", "T"],
      ["Jacob", "J"],
      ["Nephi", "N"],
      ["Enos", "E"]
    ]

The full example can be found on this plunker http://plnkr.co/edit/LK6RNzagHEEoHmMKB1Ri?p=preview

The actual problem is that the data does not sort while the user clicks the column headers. Is this the expected behaviour? Is there a way to get the data to sort when you click a column?

Thanks