Convert array to dictionary in Visual Basic

This Visual Basic example shows how to group the array of the elements into the dictionary by using the key selector

Sub main()

    Dim strArr(6) As String
    
    strArr(0) = "A"
    strArr(1) = "B"
    strArr(2) = "C"
    strArr(3) = "A"
    strArr(4) = "B"
    strArr(5) = "C"
    strArr(6) = "C"
    
    Dim groups As Object
    Set groups = ToDictionary(strArr)

    'A x 2
    'B x 2
    'C x 3
    For Each key In groups.Keys
        Debug.Print key & " x " & UBound(groups.Item(key)) + 1
    Next
    
End Sub

Function ToDictionary(arr As Variant) As Object
    
    Dim dict As Object
    Set dict = CreateObject("Scripting.Dictionary")
        
    If Not IsEmpty(arr) Then
    
        For Each elem In arr
        
            Dim group() As Variant
            Dim key As Variant
            
            key = KeySelector(elem)
            
            If dict.Exists(key) Then
                group = dict.Item(key)
                ReDim Preserve group(UBound(group) + 1)
                group(UBound(group)) = elem
                dict.Item(key) = group
            Else
                ReDim group(0)
                group(0) = elem
                dict.Add key, group
            End If
            
        Next
        
    End If

    Set ToDictionary = dict
    
End Function

'modify the key selector to work with complex structures if required
Function KeySelector(elem As Variant) As Variant
    KeySelector = elem
End Function