/// <summary>
        /// Enumerates the names of all the non-empty cells in the spreadsheet.
        /// </summary>
        public IEnumerable<String> GetNamesOfAllNonemptyCells()
        {
            Array<string> arr = new Array<string>();
            foreach (KeyValuePair<string, cell> c in DG)
            {
                if (c.Value.values != null)
                {
                    arr.add(c.Key);

                }
            }
            return arr;
        }