Friday, August 9, 2019

How to avoid using Select in Excel VBA



I've heard much about the understandable abhorrence of using .Select in Excel VBA, but am unsure of how to avoid using it. I am finding that my code would be more re-usable if I were able to use variables instead of Select functions. However, I am not sure how to refer to things (like the ActiveCell etc.) if not using Select.




I have found this article on ranges and this example on the benefits of not using select but can't find anything on how?


Answer



Some examples of how to avoid select



Use Dim'd variables



Dim rng as Range



Set the variable to the required range. There are many ways to refer to a single-cell range



Set rng = Range("A1")
Set rng = Cells(1,1)
Set rng = Range("NamedRange")


or a multi-cell range



Set rng = Range("A1:B10")

Set rng = Range("A1", "B10")
Set rng = Range(Cells(1,1), Cells(10,2))
Set rng = Range("AnotherNamedRange")
Set rng = Range("A1").Resize(10,2)


You can use the shortcut to the Evaluate method, but this is less efficient and should generally be avoided in production code.



Set rng = [A1]
Set rng = [A1:B10]



All the above examples refer to cells on the active sheet. Unless you specifically want to work only with the active sheet, it is better to Dim a Worksheet variable too



Dim ws As Worksheet
Set ws = Worksheets("Sheet1")
Set rng = ws.Cells(1,1)
With ws
Set rng = .Range(.Cells(1,1), .Cells(2,10))
End With



If you do want to work with the ActiveSheet, for clarity it's best to be explicit. But take care, as some Worksheet methods change the active sheet.



Set rng = ActiveSheet.Range("A1")


Again, this refers to the active workbook. Unless you specifically want to work only with the ActiveWorkbook or ThisWorkbook, it is better to Dim a Workbook variable too.



Dim wb As Workbook

Set wb = Application.Workbooks("Book1")
Set rng = wb.Worksheets("Sheet1").Range("A1")


If you do want to work with the ActiveWorkbook, for clarity it's best to be explicit. But take care, as many WorkBook methods change the active book.



Set rng = ActiveWorkbook.Worksheets("Sheet1").Range("A1")


You can also use the ThisWorkbook object to refer to the book containing the running code.




Set rng = ThisWorkbook.Worksheets("Sheet1").Range("A1")


A common (bad) piece of code is to open a book, get some data then close again



This is bad:



Sub foo()
Dim v as Variant

Workbooks("Book1.xlsx").Sheets(1).Range("A1").Clear
Workbooks.Open("C:\Path\To\SomeClosedBook.xlsx")
v = ActiveWorkbook.Sheets(1).Range("A1").Value
Workbooks("SomeAlreadyOpenBook.xlsx").Activate
ActiveWorkbook.Sheets("SomeSheet").Range("A1").Value = v
Workbooks(2).Activate
ActiveWorkbook.Close()
End Sub



And would be better like:



Sub foo()
Dim v as Variant
Dim wb1 as Workbook
Dim wb2 as Workbook
Set wb1 = Workbooks("SomeAlreadyOpenBook.xlsx")
Set wb2 = Workbooks.Open("C:\Path\To\SomeClosedBook.xlsx")
v = wb2.Sheets("SomeSheet").Range("A1").Value
wb1.Sheets("SomeOtherSheet").Range("A1").Value = v

wb2.Close()
End Sub


Pass ranges to your Subs and Functions as Range variables



Sub ClearRange(r as Range)
r.ClearContents
'....
End Sub


Sub MyMacro()
Dim rng as Range
Set rng = ThisWorkbook.Worksheets("SomeSheet").Range("A1:B10")
ClearRange rng
End Sub


You should also apply Methods (such as Find and Copy) to variables




Dim rng1 As Range
Dim rng2 As Range
Set rng1 = ThisWorkbook.Worksheets("SomeSheet").Range("A1:A10")
Set rng2 = ThisWorkbook.Worksheets("SomeSheet").Range("B1:B10")
rng1.Copy rng2


If you are looping over a range of cells it is often better (faster) to copy the range values to a variant array first and loop over that



Dim dat As Variant

Dim rng As Range
Dim i As Long

Set rng = ThisWorkbook.Worksheets("SomeSheet").Range("A1:A10000")
dat = rng.Value ' dat is now array (1 to 10000, 1 to 1)
for i = LBound(dat, 1) to UBound(dat, 1)
dat(i,1) = dat(i,1) * 10 'or whatever operation you need to perform
next
rng.Value = dat ' put new values back on sheet



This is a small taster for what's possible.


No comments:

Post a Comment

hard drive - Leaving bad sectors in unformatted partition?

Laptop was acting really weird, and copy and seek times were really slow, so I decided to scan the hard drive surface. I have a couple hundr...