LINQ Group By with multiple parameters

Question

I have a VB.NET application and want to do Group By on multiple columns.

Class Structure:

Public Class Person
   Public Property Name as         


        

Answer 1

Dim q1 = (From p In Repository.Table
                            Group p By p.CreatedDate.Year, p.CreatedDate.Month Into Group
                            Select New With {.Year = Year, .Month = Month, .Count = Group.Count()}).ToList

Or

Dim q2 = (From p In Repository.Table
                            Group p By key = New With {.Year = p.CreatedDate.Year, .Month = p.CreatedDate.Month} Into Group
                            Select New With {.Year = key.Year, .Month = key.Month, .Count = Group.Count()}).ToList

Answer 2

The problem is that only Key properties in anonymous types are used in equality and hashing in VB. (All properties in C# anonymous types are effectively key properties.) So you just need to change your query to:

Dim oResult = PersonList _
                .GroupBy(Function(v) New With { Key v.City, Key v.Country}) _
                .Where(Function(grp) grp.Count > 1).ToList()

See the documentation for anonymous types in VB for more details.