使用匿名类型。

Eg

group x by new { x.Column1, x.Column2 }

好的，这个是:

var query = (from t in Transactions
             group t by new {t.MaterialID, t.ProductID}
             into grp
                    select new
                    {
                        grp.Key.MaterialID,
                        grp.Key.ProductID,
                        Quantity = grp.Sum(t => t.Quantity)
                    }).ToList();

程序样例:

.GroupBy(x => new { x.Column1, x.Column2 })

虽然这个问题问的是按类属性分组，但如果你想对ADO对象(如DataTable)按多列分组，你必须将你的“新”项分配给变量:

EnumerableRowCollection<DataRow> ClientProfiles = CurrentProfiles.AsEnumerable()
                        .Where(x => CheckProfileTypes.Contains(x.Field<object>(ProfileTypeField).ToString()));
// do other stuff, then check for dups...
                    var Dups = ClientProfiles.AsParallel()
                        .GroupBy(x => new { InterfaceID = x.Field<object>(InterfaceField).ToString(), ProfileType = x.Field<object>(ProfileTypeField).ToString() })
                        .Where(z => z.Count() > 1)
                        .Select(z => z);

您还可以使用Tuple<>作为强类型分组。

from grouping in list.GroupBy(x => new Tuple<string,string,string>(x.Person.LastName,x.Person.FirstName,x.Person.MiddleName))
select new SummaryItem
{
    LastName = grouping.Key.Item1,
    FirstName = grouping.Key.Item2,
    MiddleName = grouping.Key.Item3,
    DayCount = grouping.Count(), 
    AmountBilled = grouping.Sum(x => x.Rate),
}

对于多列组，试试这个…

GroupBy(x=> new { x.Column1, x.Column2 }, (key, group) => new 
{ 
  Key1 = key.Column1,
  Key2 = key.Column2,
  Result = group.ToList() 
});

同样的方法，您可以添加Column3, Column4等。

var Results= query.GroupBy(f => new { /* add members here */  });

从c# 7开始，你也可以使用值元组:

group x by (x.Column1, x.Column2)

or

.GroupBy(x => (x.Column1, x.Column2))

.GroupBy(x => x.Column1 + " " + x.Column2)

group x by new {x. col, x. col}

.GroupBy(x => (x.MaterialID, x. producd))

需要注意的一点是，您需要为Lambda表达式发送一个对象，而不能为类使用实例。

例子:

public class Key
{
    public string Prop1 { get; set; }

    public string Prop2 { get; set; }
}

这将进行编译，但每个循环将生成一个键。

var groupedCycles = cycles.GroupBy(x => new Key
{ 
  Prop1 = x.Column1, 
  Prop2 = x.Column2 
})

如果你不想命名键属性，然后检索它们，你可以这样做。这将正确地GroupBy并为您提供关键属性。

var groupedCycles = cycles.GroupBy(x => new 
{ 
  Prop1 = x.Column1, 
  Prop2= x.Column2 
})

foreach (var groupedCycle in groupedCycles)
{
    var key = new Key();
    key.Prop1 = groupedCycle.Key.Prop1;
    key.Prop2 = groupedCycle.Key.Prop2;
}

c# 7.1或更高版本，使用元组和推断元组元素名称(目前它只适用于对象的linq，当需要表达式树时不支持，例如someIQueryable.GroupBy(…)Github的问题):

// declarative query syntax
var result = 
    from x in inMemoryTable
    group x by (x.Column1, x.Column2) into g
    select (g.Key.Column1, g.Key.Column2, QuantitySum: g.Sum(x => x.Quantity));

// or method syntax
var result2 = inMemoryTable.GroupBy(x => (x.Column1, x.Column2))
    .Select(g => (g.Key.Column1, g.Key.Column2, QuantitySum: g.Sum(x => x.Quantity)));

使用匿名类型的c# 3或更高版本:

// declarative query syntax
var result3 = 
    from x in table
    group x by new { x.Column1, x.Column2 } into g
    select new { g.Key.Column1, g.Key.Column2, QuantitySum = g.Sum(x => x.Quantity) };

// or method syntax
var result4 = table.GroupBy(x => new { x.Column1, x.Column2 })
    .Select(g => 
      new { g.Key.Column1, g.Key.Column2 , QuantitySum= g.Sum(x => x.Quantity) });

对于VB和匿名/lambda:

query.GroupBy(Function(x) New With {Key x.Field1, Key x.Field2, Key x.FieldN })