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