VBA - Speed of Hiding/Unhiding Row as a Worksheet Event - excel

Question

I'm struggling with the speed at which the following VBA code executes.
The goal of this code is to activate whenever "C4" changes, and then scan column "R" for the value 'Y'. If there's a 'Y', then it hides the row, and if not, it unhides the row. The code works, it's just not speedy - for 500 rows, it can take 30 or more seconds every time I change the value of "C4".
Does anyone have any suggestions to improve the speed at which this code executes? Or another method of accomplishing this?
Thanks for taking a look.
Private Sub Worksheet_Change(ByVal Target As Range)
Dim L As Long
Dim r As Range
L = Cells(Rows.Count, "R").End(xlUp).Row
If Not Intersect(Target, Range("C4")) Is Nothing Then
For Each r In Range("R2:R" & L)
If r.Value = "Y" Then
Rows(r.Row).Hidden = True
Else
Rows(r.Row).Hidden = False
End If
Next
End If
End Sub
In attempting to apply the suggestion below - use Union() - I have come up with the below, not working, code. Any help would be greatly appreciated.
Private Sub Worksheet_Change(ByVal Target As Range)
Dim L As Long
Dim r As Range
Dim RowsToHide As Range
Dim RowsToUnhide As Range
L = Cells(Rows.Count, "R").End(xlUp).Row
If Not Intersect(Target, Range("C4")) Is Nothing Then
For Each r In Range("R2:R" & L)
If r.Value = "Y" Then
RowsToHide = Union(RowsToHide, r.Row)
Else
RowsToUnhide = Union(RowsToUnhide, r.Row)
End If
Next
End If
RowsToHide.Hidden = True
RowsToUnhide.Hidden = False
End Sub

Answer 1

Adding Application.EnableEvents = False at the beginning of the code then turning back to true will help, Also using Applciation.ScreenUpdating = False should help as well.
Private Sub Worksheet_Change(ByVal Target As Range)
Dim L As Long
Dim r As Range
Application.EnableEvents = False
Application.ScreenUpdating = False
L = Cells(Rows.Count, "R").End(xlUp).Row
If Not Intersect(Target, Range("C4")) Is Nothing Then
For Each r In Range("R2:R" & L)
If r.Value = "Y" Then
Rows(r.Row).Hidden = True
Else
Rows(r.Row).Hidden = False
End If
Next
End If
Application.EnableEvents = True
Application.ScreenUpdating = True
End Sub

Answer 2

There are several techniques that will help speed this up
Writing to .Hidden is much slower than reading it. So check if the row is already hidden or showing before setting Hidden
Collect the rows to Hide or Show into a range (Union) and Hide/Show tehm in one go.
Private Sub Worksheet_Change(ByVal Target As Range)
Dim r As Range
Dim rngCheck As Range
Dim rngHide As Range, rngShow As Range
Application.ScreenUpdating = False
If Not Intersect(Target, Me.Range("C1")) Is Nothing Then
Set rngCheck = Me.Range(Me.Cells(1, "R"), Me.Cells(Me.Rows.Count, "R").End(xlUp))
For Each r In rngCheck.Cells
If r.Value2 = "Y" Then
If Not r.EntireRow.Hidden Then
If rngHide Is Nothing Then
Set rngHide = r.EntireRow
Else
Set rngHide = Union(rngHide, r.EntireRow)
End If
End If
Else
If r.EntireRow.Hidden Then
If rngShow Is Nothing Then
Set rngShow = r.EntireRow
Else
Set rngShow = Union(rngShow, r.EntireRow)
End If
End If
End If
Next
End If
If Not rngHide Is Nothing Then
rngHide.EntireRow.Hidden = True
End If
If Not rngShow Is Nothing Then
rngShow.EntireRow.Hidden = False
End If
Application.ScreenUpdating = True
End Sub