data-model.js

columns = [
		{
			field: 'folder.name',
			displayName: 'Folder',
			width: 200,
			enableCellEdit: false,
			groupable: true,
			visible: false,
			sortFn: Model.makeSortFunction(currentFolders)
		}
];

Model.makeSortFunction = function(currentFolders) {
    var currentSortOrder = [];
    var max = -1;
  
	angular.forEach(currentFolders, function(folder) {
		if (folder.name !== 'Uncategorized') {
			currentSortOrder[folder.name] = folder.order;
			if (folder.order > max) {
				max = folder.order;
			}
		}
	});
	
	currentSortOrder.Uncategorized = max + 1;
	
    return function(a, b) {
        return currentSortOrder[a] - currentSortOrder[b];
    }
}