Dynamically Create Dynamic Arrays in VBA - vba

Question

My objective is to use an array of names to create dynamic variables in VBA, heres the code:
Sub mymacro()
Dim names()
names = Array("cat_code()", "dog_code()", "eagle_code()")
For Each c In names
Dim c As Integer
Next
end sub
And of course my real name array has hundreds of animals so it would be rather boring doing Dim for each and every one of them. The error I'm getting is Compile Error: Duplicate declaration in current scope
What is the best feasible solution to my objective?

Answer 1

The compile error you are getting is caused by a duplicate declaration in the current scope.
In other words: this means you are declaring more than one variable with the same name.
Adding an Option Explicit statement on top of you modules requires you to declare each variable you use. It's very helpful when you receive this error because you can quickly scan your code for duplicate declaration of the highlighted line Dim <variable_name>
This is a sample demonstrating why you are getting the error:
Option Explicit
Sub Main()
Dim c As Worksheet
For Each c In Sheets
Dim c As Long ' you are going to get an error in here because
' a variable named: c, is already declared within the sub
' you can't have two variables named: c.
For c = 1 To ws.Range("A" & Rows.Count).End(xlUp).Row
' some code
Next c
Next
End Sub
There is no easy work around your problem. We would have been able to provide a better solution to your problem if you better explain what you are trying to achieve.
There is a workaround to achieve what you want but I wouldn't recommend doing it this way if you are unsure of you are actually doing ;). The below code will create a new module in your current VBA project. While iterating over the array with the animal names it will be writing new lines to Module2 so after the execution your module two will be
In order for this code to work you have to add references to Microsoft Visual Basic for Applications Extensibility 5.3". You can do that by selectingTools>>References` in the VBE window.
Also, this requires you to Trust Access to VBA Project Object Model. Go to Excel Settings >> Trust Centre >> Macros >> tick Trust Access To VBA Project Object Model.
Run the sample code.
Option Explicit
' this VBA project requires
' 1 - references to Microsoft Visual Basic For Applications Extensibility 5.3
' add it via Tools > References
'
' 2 - trust access to VBA project object model
' In spreadsheet view go to Excel(application options) >> Trust Centre >> Macro Settings
' tick the Trust Access to VBA project object model
Sub mymacro()
Dim names
names = Array("cat_code", "dog_code", "eagle_code")
Dim c As Variant
AddAModule
For Each c In names
' dynamically create arrays
WriteToModule CStr(c)
Next
CloseModule
End Sub
Private Sub AddAModule()
Dim VBProj As VBIDE.VBProject
Dim VBComp As VBIDE.vbComponent
Dim CodeMod As VBIDE.CodeModule
Set VBProj = ThisWorkbook.VBProject
Set VBComp = VBProj.VBComponents.Add(vbext_ct_StdModule)
Set CodeMod = VBComp.CodeModule
With CodeMod
.DeleteLines 1, .CountOfLines
.InsertLines 1, "Public Sub DynamicallyCreatedArrays()"
.InsertLines 2, " ' code for the sub"
End With
End Sub
Private Sub WriteToModule(arrayName As String)
With ActiveWorkbook.VBProject.VBComponents("Module2").CodeModule
.InsertLines .CountOfLines + 2, " Dim " & arrayName & " as Variant"
End With
End Sub
Private Sub CloseModule()
With ActiveWorkbook.VBProject.VBComponents("Module2").CodeModule
.InsertLines .CountOfLines + 2, "End Sub"
End With
End Sub

Answer 2

VBA can't really do what you're trying to do without getting into a horrible world of complications.
How about using a VBA Collection object instead? You'll need to create a simple class to hold the number, because VBA collections work with references, not values.
So I created a Class and set its name to "AnimalCounter", with this content:
Public Counter As Integer
Then your macro becomes something like this:
Sub mymacro()
Dim coll As New Collection
Dim c As Variant
Dim ac As AnimalCounter
For Each c In Array("cat", "dog", "eagle")
Set ac = New AnimalCounter
coll.Add ac, c
Next
Debug.Print coll("cat").Counter ' what's in "cat"?
coll("dog").Counter = coll("dog").Counter + 1 ' update "dog" by one
Debug.Print coll("dog").Counter ' "dog" should now be one more
End Sub
If you wanted arrays, put an array in to the class. Or another Collection, maybe?

Answer 3

Mike Woodhouse has the right idea of using a Collection with the keys of the animals. I add two notes:
First, I would recommend using a Dictionary instead. It is faster than a Collection, and allows explicit access to the Keys and Items collections. With a Collection, there is actually no way to fetch the keys, since the basic purpose is an ordered list of items rather than a order-agnostic hash as with a Dictionary.
For early-bound use of the Dictionary type, add a reference to Microsoft Scripting Runtime.
Second, do not use an array for the individual animals!. The reason is because arrays in VBA use by-value semantics ( see Collections in VBA – Overview, Values and References in VBA, Array Assignment Rules for more information). In short, every time you fetch an instance of an array from the containing Collection or Dictionary, you will be getting a new copy of the entire array. Thus any changes you make to the content of that array will not affect the actual array in the Dictionary or Collection. To get around this, use a Collection instead. This will use by-reference semantics and makes it much easier to append new items.
So here's what you'd want to do:
Sub ReadCodes()
Dim ws As Worksheet
Dim strAnimalName As String
Dim dctAnimalCodes As New Dictionary
Dim colAnimalCodes As Collection
Dim lngAnimalCode As Long
Set ws = Worksheets("Animal Code Data")
For iRow = 1 To ws.UsedRange.Rows.Count
strAnimalName = ws.Cells(iRow, 1)
lngAnimalCode = ws.Cells(iRow, 2)
' Easy to check if key exists
If Not dctAnimalCodes.Exists(strAnimalName) Then
Set dctAnimalCodes(strAnimalName) = New Collection
End If
' Getting the collection for this animal
Set colAnimalCodes = dctAnimalCodes(strAnimalName)
' Easy appending of new code
colAnimalCodes.Add lngAnimalCode
Next
End Sub