Error with Character Replacement VBA Function - excel

Question

Consider the following VBA Function:
Sub RemoveLetters()
Application.ScreenUpdating = False
Dim str As String: str = "abcdefghijklmnopqrstuvwxyz0123456789 "
Dim ltr As String
For i = 1 To 37
ltr = Mid(str, i, 1)
Sheet9.Range("A2:A1800").Replace _
What:=ltr, Replacement:="", MatchCase:=False, SearchFormat:=False, ReplaceFormat:=False
Next
Application.ScreenUpdating = True
End Sub
This function gets rid of all letter and number characters in a given string. However, the error I encounter is that whenever a string begins with a non-letter, non-number string it fails to execute on that string and does not execute on any further strings. That is, running into such a string stops the execution. Is there an obvious reason why this is happening? How might I modify this code to fix it?

Answer 1

For matching patterns, the best option is regular expressions or more commonly known as regex. By defining a set pattern to follow, you can extract or replace almost anything you want.
To replace all non-number and non-letter characters as well as spaces, a small function like the following works:
Function NoNormalChar(StrTarget As String) As String
Dim oRegEx As Object
Set oRegEx = CreateObject("vbscript.regexp")
With oRegEx
.Pattern = "[a-zA-Z0-9\s]+"
.Global = True
NoNormalChar = .Replace(StrTarget, "")
End With
End Function
Calling it inside a sub is simple enough:
Sub RemoveLetters()
Dim Rng As Range, Cell As Range
Application.ScreenUpdating = False
Set Rng = Sheet9.Range("A2:A1800")
For Each Cell In Rng
Cell.Value = NoNormalChar(Cell.Value)
Next Cell
Application.ScreenUpdating = True
End Sub
Copy and paste both to a single module. Run on a back-up copy and let us know of the results.