去除DataTable中重复字段

#region  去除datatable中重复字段
        /// <summary>
        /// </summary>
        /// <param name="SourceTable"></param>
        /// <param name="FieldNames"></param>
        /// <returns></returns>
        protected DataTable SelectDistinct(DataTable SourceTable, params string[] FieldNames)
        {
            object[] lastValues;
            DataTable newTable;
            DataRow[] orderedRows;
            //if (FieldNames == null || FieldNames.Length == 0)
            //    throw new ArgumentNullException("FieldNames");
            //如果FieldNames为空，则默认查询所有的列。
            if (FieldNames == null || FieldNames.Length == 0)
            {
                FieldNames = new string[SourceTable.Columns.Count];
                for (int i = 0; i < SourceTable.Columns.Count; i++)
                {
                    FieldNames[i] = SourceTable.Columns[i].ColumnName;
                }
            }
           
            lastValues = new object[FieldNames.Length];
            newTable = new DataTable();
            foreach (string fieldName in FieldNames)
                newTable.Columns.Add(fieldName, SourceTable.Columns[fieldName].DataType);
            orderedRows = SourceTable.Select("", string.Join(",", FieldNames));
            foreach (DataRow row in orderedRows)
            {
                if (!fieldValuesAreEqual(lastValues, row, FieldNames))
                {
                    newTable.Rows.Add(createRowClone(row, newTable.NewRow(), FieldNames));
                    setLastValues(lastValues, row, FieldNames);
                }
            }
            return newTable;
        }
        private bool fieldValuesAreEqual(object[] lastValues, DataRow currentRow, string[] fieldNames)
        {
            bool areEqual = true;
            for (int i = 0; i < fieldNames.Length; i++)
            {
                if (lastValues[i] == null || !lastValues[i].Equals(currentRow[fieldNames[i]]))
                {
                    areEqual = false;
                    break;
                }
            }
            return areEqual;
        }
        private DataRow createRowClone(DataRow sourceRow, DataRow newRow, string[] fieldNames)
        {
            foreach (string field in fieldNames)
                newRow[field] = sourceRow[field];
            return newRow;
        }
        private void setLastValues(object[] lastValues, DataRow sourceRow, string[] fieldNames)
        {
            for (int i = 0; i < fieldNames.Length; i++)
                lastValues[i] = sourceRow[fieldNames[i]];
        }
        #endregion