VBA row operations take too long to execute - performance

Question

So I have the script below in Execl VB that goes through the rows and deletes the ones that don't contain a certain keyword.
Sub Main()
RowsDeleted = 0
Keyword = "COLA"
For i = 2 to ActiveSheet.UsedRange.Rows.Count
If InStr(Cells(i, 1).Value, Keyword) = 0 Then
Rows(i).Delete
RowsDeleted = RowsDeleted + 1
i = i - 1
End If
Next i
MsgBox("Rows Deleted: " & RowsDeleted)
End Sub
The problem is that this script takes a very long time to execute (around 8 minutes for ~73000 entries). Why is that and how would I go about improving it?

Answer 1

no offense to other answer, but this will only help with troubleshooting.
what you need to do is remove the the line of code
Rows(i).Delete
inside the (potentially) long running For loop is what is causing the slow down.
you need to re-write it like this...
Sub Main()
RowsDeleted = 0
Keyword = "COLA"
Dim rng As Excel.Range
Dim arr() As Variant
Dim str As String
arr = ActiveSheet.UsedRange
Dim R As Long
For R = 1 To UBound(arr, 1) ' First array dimension is rows.
If InStr(arr(R, 1), Keyword) = 0 Then
If str <> "" Then
str = "," & str
End If
str = str & arr(R, 1).Address
End If
Next R
Set rng = ActiveSheet.Range(str)
RowsDeleted = rng.Rows.Count
rng.Delete
MsgBox ("Rows Deleted: " & RowsDeleted)
End Sub

Answer 2

It takes ages may due to formulas in your cells that are going to be deleted.
What you should do is to turn off auto calculation and Clear the contents of that row before delete. Also you should start from bottom up!
Try this:
Sub Main()
Dim lMode As Long
' Store initial state of Calculation mode
lMode = Application.Calculation
' Change to Manual Calculation
Application.Calculation = xlCalculationManual
' Disable screen update
Application.ScreenUpdating = False
RowsDeleted = 0
Keyword = "COLA"
' Start from bottom up!
For i = ActiveSheet.UsedRange.Rows.Count To 2 Step -1
If InStr(Cells(i, 1).Value, Keyword) = 0 Then
Rows(i).ClearContents
Rows(i).Delete
RowsDeleted = RowsDeleted + 1
End If
Next i
' Restore screenupdate and calculation mode
Application.ScreenUpdating = True
Application.Calculation = lMode
MsgBox ("Rows Deleted: " & RowsDeleted)
End Sub

Answer 3

Here could be something to look at,
It filters Column A for cells <>"Cola" and clears them
It then sorts column A so the blank cells in column A are now at the bottom
It then deletes the blank rows.
Not knowing the setup of the OP's ws, there may have to be adjustments made.
On my sample sheet I use 81,000 rows, when I run the code it takes about 5 seconds.
Sub SomeDeleteCode()
Dim Rws As Long, Rng As Range, nwRw As Long
Rws = Cells(Rows.Count, "A").End(xlUp).Row
Application.ScreenUpdating = 0
Application.Calculation = xlCalculateManual
Columns("A:A").AutoFilter Field:=1, Criteria1:="<>*Cola*"
Set Rng = Range(Cells(2, 1), Cells(Rws, 1)).SpecialCells(xlCellTypeVisible)
Rng.ClearContents
ActiveSheet.AutoFilterMode = 0
Columns(1).Sort Key1:=Range("A1"), Header:=xlYes
nwRw = Cells(Rows.Count, "A").End(xlUp).Row
Range(Range("B" & nwRw + 1), Range("B" & nwRw + 1).End(xlDown)).EntireRow.Delete
Application.Calculation = xlCalculationAutomatic
End Sub

Answer 4

Amend your code to look like this:
Sub Main()
On Error Goto ErrHandler
Application.ScreenUpdating = False
RowsDeleted = 0
Keyword = "COLA"
For i = ActiveSheet.UsedRange.Rows.Count to 2
If InStr(Cells(i, 1).Value, Keyword) = 0 Then
Rows(i).Delete
RowsDeleted = RowsDeleted + 1
' i = i - 1 ' -- manually changing the loop counter is a bad idea
End If
Next i
MsgBox("Rows Deleted: " & RowsDeleted)
EndSub:
Application.ScreenUpdating = True
exit sub
ErrHandler:
' Error handling here
resume EndSub
End Sub
The error handler is required to ensure that the ScreenUpdating is restored, even in case of an error.