VB对DataTable进行group by取max

[qiuzhilv008]

我是VB菜鸟，LINQ菜鸟，查了一上午，大都是对List且是C#的

有DATATABLE
id name
---------
a1 b3
a2 b1
a3 b2

我想取得以id分组，取max(name)该怎么写linq

sql的话就是 select max(name) from datatable group by id

[qiuzhilv008]

group by 两个项目 和 取得两个项目的该怎么写， 在group by里加,Function(y)或者直接加x("Name")试了下都编译不过 另一种方式 From k In da1 Group k By k("id") Into g = Group Select Max(g("name")) k("id")这里编译不过，Max(g("name"))这里好像也不对

[qiuzhilv008]

引用 5 楼 caozhy 的回复:

两种写法一样的。 VB的话，关键字是大写吧。你试试看。

group多项该用linq该怎么写，需要用from a in table group by这种形式，需要sum多个值

[qiuzhilv008]

Dim da1 As DataTable = New DataTable
        da1.Columns.Add("id")
        da1.Columns.Add("name")
        da1.Columns.Add("su")

Dim tem1 = From k In da1.Rows.Cast(Of DataRow)()
                   Group k By k.Item("id"), k.Item("name") Into g = Group
                   Select sum(g.item("su"))

想做以上操作该怎么写，LINQ编译不过，哪位大侠知道

[gxingmin]

   Dim da1 As DataTable = New DataTable
        da1.Columns.Add("id")
        da1.Columns.Add("name")
        da1.Columns.Add("su")

        Dim tem1 = From k In da1.Rows.Cast(Of DataRow)()
        Group k By id = k.Field(Of DataColumn)("id"), name = k.Field(Of DataColumn)("name") Into g = Group
        Select id, name

[qiuzhilv008]

引用 9 楼 gxingmin 的回复:

Visual Basic code?12345678 Dim da1 As DataTable = New DataTable da1.Columns.Add("id") da1.Columns.Add("name") da1.Columns.Add("su") Dim tem1 = From k In da1……

感谢回复！ 运行有问题：String不能转成DataColumns,另外怎么sum

[gxingmin]

 var result=
               from p in datatable 
               group p by p.id into g
               select new { name = g.Max(p => p.name) };

[qiuzhilv008]

VB的怎么写，重点是DataTable,DataTable的该是 .Item("列名")这样用吧

[threenewbee]

Dim result = datatable1.Rows.Cast(Of DataRow)().GroupBy(Function(x) x("id").ToString()).Select(Function(x) x.Max(Function(y) y["Name"].ToString()))

[qiuzhilv008]

引用 3 楼 caozhy 的回复:

Dim result = datatable1.Rows.Cast(Of DataRow)().GroupBy(Function(x) x("id").ToString()).Select(Function(x) x.Max(Function(y) y["Name"].ToString()))

谢谢，后面的y["Name"]改成y("Name")就可以了。 不过要把x("id")也取出来怎么写呢。 另外用from k into datatable group k by.. 这样该怎么写

[threenewbee]

两种写法一样的。 VB的话，关键字是大写吧。你试试看。

[gxingmin]

一直C#，VB.net真不太熟，费了半天终于成功的搞出来了

        Dim da1 As DataTable = New DataTable
        da1.Columns.Add("id")
        da1.Columns.Add("name")
        da1.Columns.Add("su", Type.GetType("System.Decimal"))

        Dim dr As DataRow = da1.NewRow()
        dr("id") = 1
        dr("name") = "张三"
        dr("su") = 10.0
        da1.Rows.Add(dr)

        dr = da1.NewRow()
        dr("id") = 1
        dr("name") = "张三"
        dr("su") = 20.0
        da1.Rows.Add(dr)

        dr = da1.NewRow()
        dr("id") = 2
        dr("name") = "张三"
        dr("su") = 30.0
        da1.Rows.Add(dr)

        dr = da1.NewRow()
        dr("id") = 1
        dr("name") = "李四"
        dr("su") = 30.0
        da1.Rows.Add(dr)

        dr = da1.NewRow()
        dr("id") = 1
        dr("name") = "李四"
        dr("su") = 40.0
        da1.Rows.Add(dr)


        Dim tem1 = From k In da1.Rows.Cast(Of DataRow)()
                   Group k By id = k.Field(Of String)("id"), name = k.Field(Of String)("name") Into g = Group, su = Sum(k.Field(Of Decimal)("su"))
                   Select id, name, su

        For Each c In tem1
            Console.WriteLine("{0},{1},{2}", c.id, c.name, c.su)
        Next

输出结果： 1,张三,30 2,张三,30 1,李四,70

[q107770540]

LINQ Group by 多列值在C#与VB.Net上写法的区别 : http://blog.csdn.net/q107770540/article/details/7629681