Question

使用以下DataTable：

    Dim d As New DataTable()
    d.Columns.Add("Product", GetType(System.String))
    d.Columns.Add("Value", GetType(System.Double))

    d.Rows.Add(New Object() {"OAP1", 100.0})
    d.Rows.Add(New Object() {"EPP4", 100})
    d.Rows.Add(New Object() {"OAP1", 150.25})
    d.Rows.Add(New Object() {"OAPIN", 200.0})

我正在尝试使用LINQ来识别是否存在多种类型的产品。在SQL中，这可以像：

SELECT Product FROM SOME_TABLE HAVING COUNT(*) > 1

我无法为我的生活找到如何在LINQ中做到这一点。我跟随的人做了这样的事情：

    Dim q = From row In d.AsEnumerable()
            Group row By New { column1 = row("Product"), column2 = row("Value") }
            Into grp
            Where grp.Count() > 1
            Select row

    For Each item In q
        ' 'q' is not declared. It may be inaccessible due to its protection level.
    Next

但是当我尝试使用'q'时出现错误。关于如何使这项工作的任何想法？

Answer 1

试试这个

Dim duplicates = d.AsEnumerable().GroupBy(Function(i) i.Field(Of String)("Product")).Where(Function(g) g.Count() > 1).Select(Function(g) g.Key)

For Each dup In duplicates
Next

Answer 2

试试

Dim q = From row in d.AsEnumerable()
        Group row By row.Field(Of String)("Product")
        Into grp
        Where grp.Count() > 1
        Select { Country = row("Product"), Value = row("Value") }

Answer 3

我不确定使用VB.NET查询语法，试试这个

Dim q = d.AsEnumerable().Select(Function(r) New With { .Column1 = r("Product"), .Column2 = r("Value")}) _
                    .GroupBy(Function(r) New With {r.Column1, r.Column2}) _
                    .Where(Function(g) g.Count() >1 )

For Each item In q
    Console.WriteLine(item.Key)
Next

LINQ to DataTable，找到重复的行

3 个答案: