Linq group by multiple column not working, lambda syntax

I am trying to group 7 objects (of Type ABPM) by date and hour and not getting correct results. 

Private Class ABPM
    Public DT As Date = Date.Now
    Public Hour As Integer = 0
    Public Minute As Integer = 0
    Public SBP As Integer = 0
    Public DBP As Integer = 0
End Class

Dim abpms As New List(Of ABPM)

The data in the list is here

The following query produces 7 groups instead of 2

Dim hourlyDayGroup2 = abpms.GroupBy(Function(a As ABPM) New With {a.DT, a.Hour})

But this one (without lambda) outputs only 2 group which is correct

Dim hourlyDayGroup = From a As ABPM In abpms _
                         Group By a.DT, a.Hour Into Group

What is the correct way to write the lambda query? Thanks

Jon Skeet
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quotationmark

You need to make your anonymous type use Key properties, so that they participate in equality computations:

Dim hourlyDayGroup2 = abpms.GroupBy(Function(a As ABPM) New With {Key a.DT, Key a.Hour})

From MSDN:

Key properties differ from non-key properties in several fundamental ways:

  • Only the values of key properties are compared in order to determine whether two instances are equal.
  • The values of key properties are read-only and cannot be changed.
  • Only key property values are included in the compiler-generated hash code algorithm for an anonymous type.

Note that in C#, all properties of anonymous types have the same semantics as key properties in VB.

people

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