body 用戶數 p s 類型 data span bsp class res

https://www.cnblogs.com/johnblogs/p/6006867.html

DataTable ds = new DataTable();

//1、lamda 表達式寫法（推薦）
var result = ds.AsEnumerable().GroupBy(s => new{Year = s.Field<int>("Year"), Month = s.Field<int>("Month"), Day = s.Field<int>("Day")});

//2、Linq寫法 最終編譯器會把它轉化為lamda表達式
//var result = from s in ds.Tables[0].AsEnumerable()
group s by new { Year = s.Field<int>("Year"), Month = s.Field<int>("Month"), Day = s.Field<int>("Day") } into temp

select temp;

//DataTable 使用GroupBy方法需要註意result為IGrouping<int,DataRow>類型
foreach (var thisGroup in result)
{
foreach (var row in thisGroup)
{
//遍歷當前這組的所有row
}
}

//統計不重復的數量，沒測試不知是否能用 dt.DefaultView.ToTable(true, new string[1] { "UserName" }).Rows.Count; http://www.xuebuyuan.com/1990057.html using (DataTable dt = ds.Tables[0])
{
//三個變量分別記錄總記錄數、不重復的用戶數、所有用戶的金額總額
int rowsCount, distinctUserRowsCount, AllUserMoney;
rowsCount = dt.Rows.Count;
distinctUserRowsCount = dt.DefaultView.ToTable(true, new string[1] { "UserName" }).Rows.Count;
AllUserMoney = Convert.ToDecimal(dt.Compute("sum(UserMoney)", ""));
}

C#DataTable 使用GroupBy方法的lamda 表達式和Linq語句寫法