在DataTable中实现DataTable.Select("Distinct")功能

我们有时候需要对DataTable中数据进行Distinct处理，过滤掉重复的数据，本文给出了解决方法：

事例代码来源于: Erik Porter's Blog   Select DISTINCT on DataTable http://weblogs.asp.net/eporter/archive/2005/02/10/370548.aspx 以及 HOWTOVisualC # .NET 中实现 DataSet SELECTDISTINCT Helper 类 http://support.microsoft.com/?id=326176
 

/**/ /// <summary>
        /// 返回执行Select distinct后的DataTable
        /// </summary>
        /// <param name="SourceTable">源数据表</param>
        /// <param name="FieldNames">字段集</param>
        /// <returns></returns>
         private  DataTable SelectDistinct(DataTable SourceTable,  params   string [] FieldNames)
         {
            object[] lastValues;
            DataTable newTable;
            DataRow[] orderedRows;

            if (FieldNames == null || FieldNames.Length == 0)
                throw new ArgumentNullException("FieldNames");

            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]];
        }  

使用:

DataTable dt = (System.Data.DataTable) this .ViewState[ " Mydt " ];
             string [] fileds = {"Filed1","Filed2"} ; // DISTINCT字段数组
            DataTable newdt = this .SelectDistinct(dt,fileds); // 返回过滤后的DataTable