Running Worksheet_Change on top of itself intentionally - excel

Question

Skip my rambling narrative by scrolling down to tldr and Question.
I have several rows and columns with values; e.g. A10:G15. In each row, the value of the cell immediately to the right of any cell is dependent on that cell up to the extents of the columns involved. In this manner, the value of a cell immediately to the right of any cell is always numerically larger than the cell or blank if the original cell is blank.
To maintain this dependency, I want to clear any values to the right if I clear the value from a cell within A:F or progressively add a random number to the remaining cells to the right if I input a new value into any cell within A:F.
Sample data. The 7 in the top-left is A10.
A B C D E F G
7 12 15 19 23 27 28
4 6 10 14 17 18 22
8 10 14 18 23 26 31
8 13 15 18 22 25 30
8 13 16 18 19 21 24
0 3 4 9 10 12 16
'similar data in A19:G22 and A26:G30
tldr
▪ If I clear D12, E12:G12 should also be cleared.
▪ If I type a new value into C14 then D14:G14 should each receive a new value which is random but larger than the previous value.
▪ I might want to clear or paste in several values in a column and would expect the routine to deal with each in turn.
▪ I have several of these non-contiguous regions (see Union'ed range in code sample below) and would prefer a DRY coding style.
Code
Option Explicit
Private Sub Worksheet_Change(ByVal Target As Range)
'Debug.Print Target.Address(0, 0)
If Not Intersect(Target, Range("A10:F15, A19:F22, A26:F30")) Is Nothing Then
Dim t As Range
For Each t In Intersect(Target, Range("A10:F15, A19:F22, A26:F30"))
If IsEmpty(t) Then
t.Offset(0, 1).ClearContents
ElseIf Not IsNumeric(t) Then
t.ClearContents
Else
If t.Column > 1 Then
If t <= t.Offset(0, -1) Or IsEmpty(t.Offset(0, -1)) Then
t.ClearContents
Else
t.Offset(0, 1) = t + Application.RandBetween(1, 5)
End If
Else
t.Offset(0, 1) = t + Application.RandBetween(1, 5)
End If
End If
Next t
End If
End Sub
Code explanation
This event driven Worksheet_Change deals with each cell that has changed but only modifies the cell directly to the right, not the remaining cells in that row. The job of maintaining the remaining cells is achieved by leaving event triggers active so that when that single cell to the right is modified, the Worksheet_Change triggers an event that calls itself with a new Target.
Question
The above routine seems to run fine and I have yet to destabilize my project environment despite my best/worst efforts. So what's wrong with intentionally running a Worksheet_Change on top of itself if the reiteration cycles can be controlled to a finite result?

Answer 1

I would argue that what is wrong with recursively triggering the change event is that this way Excel can only sustain a pretty tiny call stack. At 80 calls it killed my Excel instance. When I outsourced the recursion I at least got to a little over 1200 calls, of course adding redundancy to some extent:
Option Explicit
Const RANGE_STR As String = "A10:F15, A19:F22, A26:F30"
Private Sub Worksheet_Change(ByVal target As Range)
Application.EnableEvents = False
Dim t As Range
If Not Intersect(target, Range(RANGE_STR)) Is Nothing Then
For Each t In Intersect(target, Range(RANGE_STR))
makeChange t
Next t
End If
Application.EnableEvents = True
End Sub
Sub makeChange(ByVal t As Range)
If Not Intersect(t, Range(RANGE_STR)) Is Nothing Then
If IsEmpty(t) Then
t.Offset(0, 1).ClearContents
makeChange t.Offset(0, 1)
ElseIf Not IsNumeric(t) Then
t.ClearContents
makeChange t
Else
If t.Column > 1 Then
If t <= t.Offset(0, -1) Or IsEmpty(t.Offset(0, -1)) Then
t.ClearContents
makeChange t
Else
t.Offset(0, 1) = t + Application.RandBetween(1, 5)
makeChange t.Offset(0, 1)
End If
Else
t.Offset(0, 1) = t + Application.RandBetween(1, 5)
makeChange t.Offset(0, 1)
End If
End If
End If
End Sub

Answer 2

I don't think you need recursive calls, read by area, by row, into array, change array and write back to sheet:
Const RANGE_STR As String = "A10:F15, A19:F22, A26:F30"
Private Sub Worksheet_Change(ByVal Target As Range)
Dim MyArr As Variant, TargetR As Long, TargetC As Long, i As Long, ar As Range, myRow As Range
Dim minC As Long, maxC As Long
If Not Intersect(Target, Range(RANGE_STR)) Is Nothing Then
minC = Range(RANGE_STR).Column 'taken form first area
maxC = 1 + Range(RANGE_STR).Columns.Count 'taken form first area
For Each ar In Target.Areas
TargetC = ar.Column
For Each myRow In ar.Rows
TargetR = myRow.Row
MyArr = Range(Cells(TargetR, minC), Cells(TargetR, maxC))
If IsEmpty(MyArr(1, TargetC)) Or Not IsNumeric(MyArr(1, TargetC)) Then
For i = TargetC To UBound(MyArr, 2)
MyArr(1, i) = Empty
Next i
Else
For i = TargetC + 1 To UBound(MyArr, 2)
MyArr(1, i) = MyArr(1, i - 1) + Application.RandBetween(1, 5)
Next i
End If
If Not Intersect(Range(Cells(TargetR, minC), Cells(TargetR, maxC)), Range(RANGE_STR)) Is Nothing Then
Application.EnableEvents = False
Range(Cells(TargetR, minC), Cells(TargetR, maxC)) = MyArr
Application.EnableEvents = True
End If
Next myRow
Next ar
End If
End Sub