内存表建立关联后求平均的问题。

[蘑菇]

dataset下有两个表a，b
a表
id，date，值

b表
id，date，值

想建立一个关联让a.id=b.id and a.date=b.date
然后求avg（a.值-b.值） 按照date分组
如何实现呢？
还有就是求abs（a.值-b.值）<1的个数，以及abs（a.值-b.值）<1个数在总个数中的百分比。如何实现呢？有没有好的思路。谢谢。

[lhblxm]

用LINQ

[lhblxm]

' Fill the DataSet.
Dim ds As New DataSet()
ds.Locale = CultureInfo.InvariantCulture
' See the FillDataSet method in the Loading Data Into a DataSet topic.
FillDataSet(ds)

Dim orders As DataTable = ds.Tables("SalesOrderHeader")
Dim details As DataTable = ds.Tables("SalesOrderDetail")


Dim query = _
From order In orders.AsEnumerable() _
Join detail In details.AsEnumerable() _
On order.Field(Of Integer)("SalesOrderID") Equals _
detail.Field(Of Integer)("SalesOrderID") _
Where order.Field(Of Boolean)("OnlineOrderFlag") = True And _
order.Field(Of DateTime)("OrderDate").Month = 8 _
Select New With _
{ _
.SalesOrderID = order.Field(Of Integer)("SalesOrderID"), _
.SalesOrderDetailID = detail.Field(Of Integer)("SalesOrderDetailID"), _
.OrderDate = order.Field(Of DateTime)("OrderDate"), _
.ProductID = detail.Field(Of Integer)("ProductID") _
}

For Each order In query
Console.WriteLine(order.SalesOrderID & vbTab & _
order.SalesOrderDetailID & vbTab & _
order.OrderDate & vbTab & _
order.ProductID)
Next

MSDN上的示例

[蘑菇]

能具体点吗？LINQ我不太会啊。