在DataTable中实现DataTable.Select("Distinct")功能/数组的方式实现DataTable中的distinct

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

-======================================================================================

M_id, M_name两个字段数据相同的DataRow必须是连续的，不能被分隔

string sql = string.Format("select M_id, M_name from dbo.BusinessWaitTable order by M_id, M_name");

DataTable dt = GetDataTable(sql);

//得出datatable中所有行放入数组
DataRow[] drs = dt.Select();

//存放过滤后DataRow的可变长度数组
ArrayList al = new ArrayList();

//源数组不为空，开始过滤
if (drs.Length != 0)
{
//先加入源数组第一个元素
al.Add(drs[0]);

/*遍历源数组元素，
* 将与目标数组最后一个元素不同的源数组元素加入到目标数组*/
for (int i = 0; i < drs.Length; i++)
{
if (drs[i]["M_id"].ToString() != ((DataRow)al[al.Count - 1])["M_id"].ToString()
&& drs[i]["M_name"].ToString() != ((DataRow)al[al.Count - 1])["M_name"].ToString())
{
al.Add(drs[i]);
}
}
}

2 用数组的方式实现DataTable中的distinct