Running Worksheet_Change on top of itself intentionally
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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 topleft 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
▪ 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 noncontiguous regions (see Union'ed range in code sample
below) and would prefer a DRY coding style.
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
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.
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?
2 answers

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

I don't think you need recursive calls, read by area, by row, into array, change array and write back to sheet:
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 For Each ar In Target.Areas TargetC = ar.Column For Each myRow In ar.Rows TargetR = myRow.Row MyArr = Range(Cells(TargetR, 1), Cells(TargetR, 7)) 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 Application.EnableEvents = False If Not Intersect(Range(Cells(TargetR, 1), Cells(TargetR, 7)), Range("A10:F15, A19:F22, A26:F30")) Is Nothing Then Range(Cells(TargetR, 1), Cells(TargetR, 7)) = MyArr End If Application.EnableEvents = True Next myRow Next ar End Sub