Excel VBA - For Loop taking far too long to execute - vba

Question

I have a script which I have designed in order to hide rows that do not contain data, the script looks through column A starting from Row 7. If it finds rows that do not contain values, it will hide those rows from sight. Unfortunately this script takes over 1 minute to run on large sheets in its present form.
Does anybody have suggestions on how to re-write this script in order to make it faster? It needs to run in 5 seconds max
Sub hideAllRows()
Dim Checklist As Variant
UnlockSheet
Call Show_Hide("Row", "7:519", True)
Call Show_Hide("Row", "529:1268", True)
Checklist = ActiveSheet.Range("A1:A" & Cells(Rows.Count, "A").End(xlUp).Row).Value
For I = UBound(Checklist, 1) To LBound(Checklist, 1) Step -1
If Checklist(I, 1) <> "" Then
Rows(I & ":" & I).Select
Selection.EntireRow.Hidden = False
End If
Next I

Answer 1

I have edited your code in order to make things simpler.
One of the issues is that your code is firing events "like crazy" (each time you do a Select, an event is fired).
A. If you want to use your code as is, I suggest you add at the beginning
Application.EnableEvents = False
and add in the last line:
Application.EnableEvents = true
B. I suggest that you do the hiding "in one blow", after the loop has ended. Here is how:
Dim Checklist As Variant
dim sRowsToHide as string
UnlockSheet
Application.ScreenUpdating = False
Call Show_Hide("Row", "7:519", True)
Call Show_Hide("Row", "529:1268", True)
Checklist = ActiveSheet.Range("A1:A" & Cells(Rows.Count, "A").End(xlUp).Row).Value
For I = UBound(Checklist, 1) To LBound(Checklist, 1) Step -1
If Checklist(I, 1) <> "" Then
if sRowsToHide = "" then
sRowsToHide = I & ":" & I
else
sRowsToHide = sRowsToHide & "," & I & ":" & I
end if
End If
Next I
ActiveSheet.Range(sRowsToHide).EntireRow.Hidden = True
Application.ScreenUpdating = True
You can use the following line to see how such a thing would work:
ActiveSheet.Range("2:2,14:14,17:17,19:19").EntireRow.Hidden = True

Answer 2

You can try using ScreenUpdating, it will only update the sheet once the loop is done instead of updating every time
Dim Checklist As Variant
UnlockSheet
Application.ScreenUpdating = False
Call Show_Hide("Row", "7:519", True)
Call Show_Hide("Row", "529:1268", True)
Checklist = ActiveSheet.Range("A1:A" & Cells(Rows.Count, "A").End(xlUp).Row).Value
For I = UBound(Checklist, 1) To LBound(Checklist, 1) Step -1
If Checklist(I, 1) <> "" Then
Rows(I & ":" & I).Select
Selection.EntireRow.Hidden = False
End If
Next I
Application.ScreenUpdating = True

Answer 3

The following will hide all rows that have constants (e.g. typed values) in column A.
Sub hide_A_values()
With ActiveSheet.Columns("A")
.SpecialCells(xlCellTypeConstants).EntireRow.Hidden = True
End With
End Sub
This next one will hide all rows that have formulas in column A.
Sub hide_A_values()
With ActiveSheet.Columns("A")
.SpecialCells(xlCellTypeFormulas).EntireRow.Hidden = True
End With
End Sub
Finally, this will hide all rows that have constants (e.g. typed values) or formulas in column A.
Sub hide_A_values()
With ActiveSheet.Columns("A")
Union(.SpecialCells(xlCellTypeConstants), .SpecialCells(xlCellTypeFormulas)).EntireRow.Hidden = True
End With
End Sub
The problem is that you have to provide error control or risk dealing with the dreaded Runtime error: 1004 No cells were found if there are no constants or formulas to hide. On Error Resume Next typically takes care of this.
Sub hide_A_values()
With ActiveSheet.Columns("A")
On Error Resume Next
.SpecialCells(xlCellTypeConstants).EntireRow.Hidden = True
.SpecialCells(xlCellTypeFormulas).EntireRow.Hidden = True
On Error GoTo 0
End With
End Sub
The only case not covered by those is formulas returning empty strings (e.g. "") which are not considered truly blank.