Excel VBA For Loop Optimization - Exit when j = 2 - excel

Question

I'm trying to optimize code that will delete rows that meet certain criteria. I have working code, but the following code creates 7 seconds of wait time to execute:
Dim j As Long
For j = 2 To Rows.Count
If (Range("J" & j).Value <> "") Then
Range("A" & j & ":R" & j).Select
Selection.Delete Shift:=xlUp
End If
Next j
The following code runs instantly; however, I can't get it to work once j = 2. What code needs to be added to stop the loop before it deletes the column headers in row 1?
' Delete rows where column J is not blank
For j = Range("J" & Rows.Count).End(xlUp).Row To 1 Step -1
If (Range("J" & j).Value <> "") Then
Range("A" & j & ":R" & j).Select
Selection.Delete Shift:=xlUp
End If
Next j

Answer 1

As mentioned in the comments, you should looking backward for deletions. If you do the deletions from row#2 to the last row, there might be some rows should be deleted but remained there. Take this for example, assuming we are going to delete row#3 and row#4. If we do it forward, the row#4 becomes to new row#3 after deleting old row#3. And the next row to be checked is row#4, that is the original row#5. So the data in row#4 is actually in row#3 now and it'll never be deleted.
However, when your data is quite massive, the deletions would take so many resource that it drags down the speed. It would be better to find all the ranges to be deleted and delete them at once in the end. We can do it by Union method. And this can also prevent the problem mentioned before, so we can do it forward as other loops.
Lastly, you can avoid selecting ranges since it is not so efficient. Range().Delete can simply delete the range and without selecting it.
The code would be like this.
'pseudo code
Sub deletion()
For i = 2 To lastrow
If shouldBeDeleted Then
If deletingRng Is Nothing Then
Set deletingRng = Cells(i, X)
Else
Set deletingRng = Union(deletingRng, Cells(i, X)
End If
End If
Next i
deletingRng.Delete Shift:=xlUp
End Sub