Aggregating Objects in Collection

monserob
monserob used Ask the Experts™
on
I have a custom collection that inherits from List(of T) that is used to store objects that expose item no, qty and price properties.

What I want to do is summarise the quantities in a data grid based on item no and price so for example if my objects hold the following information for item no, qty and price:

a, 1, 10.00
a, 1, 10.00
b, 1, 20.00
a, 1, 50.00
a, 1, 10.00

I would show the following in the grid

a, 3, 10.00
a, 1, 50.00
b, 3, 20.00

What's the best way to do this in VB.Net? I've been looking at the Group By in LINQ but most examples are in C# and I'm struggling to get things to work.
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Glanced up at my screen and thought I had coded the Matrix...  Turns out, I just fell asleep on the keyboard.
Most Valuable Expert 2011
Top Expert 2015
Commented:
See if this works for you. Please feel free to ask further questions if you require any clarification  = )

Module Module1

    Sub Main()
        Dim aList As New List(Of ObjectsWhichExpose)

        aList.Add(New ObjectsWhichExpose() With {.ItemNo = "a", .Quantity = 1, .Price = 10.0})
        aList.Add(New ObjectsWhichExpose() With {.ItemNo = "a", .Quantity = 1, .Price = 10.0})
        aList.Add(New ObjectsWhichExpose() With {.ItemNo = "b", .Quantity = 1, .Price = 20.0})
        aList.Add(New ObjectsWhichExpose() With {.ItemNo = "a", .Quantity = 1, .Price = 50.0})
        aList.Add(New ObjectsWhichExpose() With {.ItemNo = "a", .Quantity = 1, .Price = 10.0})

        Dim query = From item In aList _
                    Group item By item.ItemNo, item.Price Into Group _
                    Order By ItemNo _
                    Select New With {.ItemNo = ItemNo, .Quantity = Group.Sum(Function(x As ObjectsWhichExpose) x.Quantity), .Price = Price}

        For Each item In query
            Console.WriteLine("{0}, {1}, {2}", item.ItemNo, item.Quantity, item.Price)
        Next

        Console.ReadKey()
    End Sub

End Module

Public Class ObjectsWhichExpose


    Private _itemNo As String
    Public Property ItemNo() As String
        Get
            Return _itemNo
        End Get
        Set(ByVal value As String)
            _itemNo = value
        End Set
    End Property


    Private _qty As Integer
    Public Property Quantity() As Integer
        Get
            Return _qty
        End Get
        Set(ByVal value As Integer)
            _qty = value
        End Set
    End Property


    Private _price As Double
    Public Property Price() As Double
        Get
            Return _price
        End Get
        Set(ByVal value As Double)
            _price = value
        End Set
    End Property


End Class

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Author

Commented:
That's great thanks!

Before I mark as accepted can I ask whether there's an easy of associating the grouped objects with the underlying objects in the collection e.g. if the user was to delete a summary row in the grid I would need to find the individual objects that were grouped on that row and remove them from the collection. Would this be another LINQ to Object?

Author

Commented:
I've not received a response, which is a pity but in fairness a solution to the original question has been provided so I will mark as accepted.

If I run into difficulties with removing the objects that belong to a summarised row I'll post a new question

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