Change value of an item in a collection in a dictionary - excel

Question

I'm trying to create a dictionary which has a collection for every key. The reason for this is that I want to retrieve several values from the same key later on. In this example I want to have the total value (val) of a unique key as well as the number of occurrences (n):
sub update()
Dim dict As Dictionary
Dim coll As Collection
Set dict = New Dictionary
Set coll = New Collection
coll.Add 100, "val"
coll.Add 3, "n"
dict.Add "coll", coll
Debug.Print dict.item("coll")("val")
Debug.Print dict.item("coll")("n")
This works fine so far, the problem occurs when I try to update the value in the collection (object doesn't support this):
dict.item("coll")("val") = dict.item("coll")("val") + 100
What I tried:
If I use an array instead of the collection, there is no error but the value doesn't change.
It only works if I read out the collection to variables, change the value, create a new collection, remove the old from the dictionary and add the new collection.
Is there any way to do it like my approach above in a single line?
I would also be happy for an alternative solution to the task.

Answer 1

Once you added an item to the collection, you cannot change it that easily. Such expression:
coll("n") = 5
will cause Run-time error '424': Object required.
You can check it by yourself on the simple example below:
Sub testCol()
Dim col As New VBA.Collection
Call col.Add(1, "a")
col("a") = 2 '<-- this line will cause Run-time error '424'
End Sub
The only way to change the value assigned to the specified key in the given collection is by removing this value and adding another value with the same key.
Below is the simple example how to change the value assigned to a collection with key [a] from 1 to 2:
Sub testCol()
Dim col As New VBA.Collection
With col
Call .Add(1, "a")
Call .Remove("a")
Call .Add(2, "a")
End With
End Sub
Below is your code modified in order to allow you to change the value assigned to the given key in the collection:
Sub update()
Dim dict As Dictionary
Dim coll As Collection
Set dict = New Dictionary
Set coll = New Collection
coll.Add 100, "val"
coll.Add 3, "n"
dict.Add "coll", coll
Debug.Print dict.Item("coll")("val")
Debug.Print dict.Item("coll")("n")
'This works fine so far, the problem occurs when I try to update the value in the collection (object doesn't support this):
Dim newValue As Variant
With dict.Item("coll")
newValue = .Item("val") + 100
On Error Resume Next '<---- [On Error Resume Next] to avoid error if there is no such key in this collection yet.
Call .Remove("val")
On Error GoTo 0
Call .Add(newValue, "val")
End With
End Sub

Answer 2

It is not elegant perhaps, but maybe you can write a sub to update a collection by a key:
Sub UpdateCol(ByRef C As Collection, k As Variant, v As Variant)
On Error Resume Next
C.Remove k
On Error GoTo 0
C.Add v, k
End Sub
Used like this:
Sub Update()
Dim dict As Dictionary
Dim coll As Collection
Set dict = New Dictionary
Set coll = New Collection
coll.Add 100, "val"
coll.Add 3, "n"
dict.Add "coll", coll
Debug.Print dict.Item("coll")("val")
Debug.Print dict.Item("coll")("n")
UpdateCol dict.Item("coll"), "val", dict.Item("coll")("val") + 100
Debug.Print dict.Item("coll")("val")
End Sub
With output as expected:
100
3
200

Answer 3

Here is an approach using a User Defined Object (Class). Hoepfully you can adapt this to your problem.
Rename the Class Module cMyStuff or something else meaningful.
Class Module
Option Explicit
Private pTotalVal As Long
Private pCounter As Long
Public Property Get TotalVal() As Long
TotalVal = pTotalVal
End Property
Public Property Let TotalVal(Value As Long)
pTotalVal = Value
End Property
Public Property Get Counter() As Long
Counter = pCounter
End Property
Public Property Let Counter(Value As Long)
pCounter = Value
End Property
Regular Module
Option Explicit
Sub Update()
Dim cMS As cMyStuff, dMS As Dictionary
Dim I As Long
Set dMS = New Dictionary
For I = 1 To 3
Set cMS = New cMyStuff
With cMS
.Counter = 1
.TotalVal = I * 10
If Not dMS.Exists("coll") Then
dMS.Add "coll", cMS
Else
With dMS("coll")
.TotalVal = .TotalVal + cMS.TotalVal
.Counter = .Counter + 1
End With
End If
End With
Next I
With dMS("coll")
Debug.Print "Total Value", .TotalVal
Debug.Print "Counter", .Counter
End With
End Sub
Results in Immediate Window
Total Value 60
Counter 3