Create dictionary of lists in vba

Question

I have worked in Python earlier where it is really smooth to have a dictionary of lists (i.e. one key corresponds to a list of stuff). I am struggling to achieve the same in

Answer 1

I am not that familiar with C++ and Python (been a long time) so I can't really speak to the differences with VBA, but I can say that working with Arrays in VBA is not especially complicated.

In my own humble opinion, the best way to work with dynamic arrays in VBA is to Dimension it to a large number, and shrink it when you are done adding elements to it. Indeed, Redim Preserve, where you redimension the array while saving the values, has a HUGE performance cost. You should NEVER use Redim Preserve inside a loop, the execution would be painfully slow

Adapt the following piece of code, given as an example:

Sub CreateArrays()

Dim wS As Worksheet
Set wS = ActiveSheet

Dim Flanged_connections()
ReDim Flanged_connections(WorksheetFunction.CountIf(wS.Columns(1), _
    "Flanged_connections"))

For i = 1 To wS.Cells(1, 1).CurrentRegion.Rows.Count Step 1

    If UCase(wS.Cells(i, 1).Value) = "FLANGED_CONNECTIONS" Then   ' UCASE = Capitalize everything

        Flanged_connections(c1) = wS.Cells(i, 2).Value

    End If

Next i

End Sub

Answer 2

You can have dictionaries within dictionaries. No need to use arrays or collections unless you have a specific need to.

Sub FillNestedDictionairies()

    Dim dcParent As Scripting.Dictionary
    Dim dcChild As Scripting.Dictionary
    Dim rCell As Range
    Dim vaSplit As Variant
    Dim vParentKey As Variant, vChildKey As Variant

    Set dcParent = New Scripting.Dictionary

    'Don't use currentregion if you have adjacent data
    For Each rCell In Sheet2.Range("A1").CurrentRegion.Cells
        'assume the text is separated by a space
        vaSplit = Split(rCell.Value, Space(1))

        'If it's already there, set the child to what's there
        If dcParent.Exists(vaSplit(0)) Then
            Set dcChild = dcParent.Item(vaSplit(0))
        Else 'create a new child
            Set dcChild = New Scripting.Dictionary
            dcParent.Add vaSplit(0), dcChild
        End If
        'Assumes unique post-space data - text for Exists if that's not the case
        dcChild.Add CStr(vaSplit(1)), vaSplit(1)
    Next rCell

    'Output to prove it works
    For Each vParentKey In dcParent.Keys
        For Each vChildKey In dcParent.Item(vParentKey).Keys
            Debug.Print vParentKey, vChildKey
        Next vChildKey
    Next vParentKey

End Sub

Answer 3

Arrays in VBA are more or less like everywhere else with various peculiarities:

• Redimensioning an array is possible (although not required).
• Most of the array properties (e.g., Sheets array in a Workbook) are 1-based. Although, as rightly pointed out by @TimWilliams, the user-defined arrays are actually 0-based. The array below defines a string array with a length of 11 (10 indicates the upper position).

Other than that and the peculiarities regarding notations, you shouldn't find any problem to deal with VBA arrays.

Dim stringArray(10) As String
stringArray(1) = "first val"
stringArray(2) = "second val"
'etc.

Regarding what you are requesting, you can create a dictionary in VBA and include a list on it (or the VBA equivalent: Collection), here you have a sample code:

Set dict = CreateObject("Scripting.Dictionary")
Set coll = New Collection
coll.Add ("coll1")
coll.Add ("coll2")
coll.Add ("coll3")
If Not dict.Exists("dict1") Then
    dict.Add "dict1", coll
End If

Dim curVal As String: curVal = dict("dict1")(3) '-> "coll3"

Set dict = Nothing