如何在LINQ中做GroupBy多列
SQL中类似的代码:
SELECT * FROM <TableName> GROUP BY <Column1>,<Column2>
如何将其转换为LINQ:
QuantityBreakdown
(
MaterialID int,
ProductID int,
Quantity float
)
INSERT INTO @QuantityBreakdown (MaterialID, ProductID, Quantity)
SELECT MaterialID, ProductID, SUM(Quantity)
FROM @Transactions
GROUP BY MaterialID, ProductID
当前回答
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) });
其他回答
.GroupBy(x => 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);
程序样例:
.GroupBy(x => new { x.Column1, x.Column2 })
.GroupBy(x => (x.MaterialID, x. producd))
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) });
