Can I loop through key/value pairs in a VBA collection? - vba

Question

In VB.NET, I can iterate through a dictionary's key/value pairs:
Dictionary<string, string> collection = new Dictionary<string, string>();
collection.Add("key1", "value1");
collection.Add("key2", "value2");
foreach (string key in collection.Keys)
{
MessageBox.Show("Key: " + key + ". Value: " + collection[key]);
}
I know in VBA I can iterate through the values of a Collection object:
Dim Col As Collection
Set Col = New Collection
Dim i As Integer
Col.Add "value1", "key1"
Col.Add "value2", "key2"
For i = 1 To Col.Count
MsgBox (Col.Item(i))
Next I
I also know that I do this with a Scripting.Dictionary VBA object, but I was wondering if this is possible with collections.
Can I iterate through key/value pairs in a VBA collection?

Answer 1

you cannot retrieve the name of the key from a collection. Instead, you'd need to use a Dictionary Object:
Sub LoopKeys()
Dim key As Variant
'Early binding: add reference to MS Scripting Runtime
Dim dic As Scripting.Dictionary
Set dic = New Scripting.Dictionary
'Use this for late binding instead:
'Dim dic As Object
'Set dic = CreateObject("Scripting.Dictionary")
dic.Add "Key1", "Value1"
dic.Add "Key2", "Value2"
For Each key In dic.Keys
Debug.Print "Key: " & key & " Value: " & dic(key)
Next
End Sub

Answer 2

This answwer is not iterating over keys of a collection - which seems to be impossible, but gives some more workarounds if you do not want to use a Dictionary.
You can do a collection of KeyValues as outlined in https://stackoverflow.com/a/9935108/586754 . (Create keyvalue class and put those into the collection.)
In my (non Excel but SSRS) case I could not add a class and did not want to add a .net reference.
I used 2 collections, 1 to store keys and 1 to store values, and then kept them in sync when adding or deleting.
The following shows the add as an example - though it is limited to string/int key/value, and the int value s not stored but added to previous values, which was needed for me aggregating values in SSRS. This could be easily modified though to not add but store values.
ck key collection, cv value collection.
Private Sub StoreAdd(ck As Collection, cv As Collection, k As String, v As Integer)
Dim i As Integer
Dim found As Boolean = false
Dim val As Integer = v
For i = 1 to ck.Count
if k = ck(i)
' existing, value is present
val = val + cv(i)
' remove, will be added later again
ck.Remove(i)
cv.Remove(i)
End If
if i <= ck.Count
' relevant for ordering
If k > ck(i)
' insert at appropriate place
ck.Add(k, k, i)
cv.Add(val, k, i)
found = true
Exit For
End If
End If
Next i
if not found
' insert at end
ck.Add(k, k)
cv.Add(val, k)
End If
End Sub