macro in VBA to get prefixes - excel

Question

in my job I have very often to create prefixes. Since last week I think that I can do faster my job with a Macro in excel, but I never have developed in VBA before and need your help.
We get a list with article numbers from any supplier and then I have to create the prefixes for our System. Our System is looking for the prefix and then it knows the supplier. If the first 6 chars are exactly the same with another supplier, so the prefixes from both supplier is getting longer to 7 chars. If it's the same again, the prefix is getting an eight char and so on.
Example:
article numbers from supplier_1:
04012384724993
04012384473373
04012384111453
...
article numbers from supplier_2:
12345671846219
12345629946120
12345629815294
...
article numbers from supplier_3:
12345694724109
12345694715268
12345694724773
...
Now you see that first chars from each supplier are the same.
For Supplier_1 all numbers beginning with "040123", so that's the first prefix.
Supplier_2 ans 3 have the same first 6 chars, so here we use one more to identificate him.
Supp_2 -> "1234567" and "1234562"
Supp_3 -> "1234569"
Supplier_2 have now 2 prefixes, because the 7th position is different in some article numbers, but not the same like supplier_3 is using at this position.
Now I have an excel sheet with column A and B.
In column A I paste all article numbers from supplier_1 and in column B I paste these from supplier_2.
Now I want to run a macro, that create a variable "search" with the first 6 chars from Cell A1 and check it against Column B. If one of the numbers in Column B is the same then variable "search" get additional the next char from Cell A1 and check again. If now the first 7 chars couldn't be found in Column B, it's the first prefix from supplier_1. I want to paste it into column D.
Now the variale "search" get the first 6 chars from the next Cell in column A, (A2), later A3, ... and check it against Column B.
I don't know, how to get the first 6 chars into the variable "search".
Can someone help me please?
Thank you very much.

Answer 1

It is always a good idea to approach big problems in as small chunks as possible. Indeed, it may be a good start to assign the first few characters of a string to a variable. A quick Google search would most likely point you to the Left function. Here's a link to the MSDN page for more information on how it works and how to use it.
I also suggest that you enable the Immediate Window, which can be done with Ctrl + G by default. Using Debug.Print will be one of your strongest tools while writing new code.
Sub Example1()
Dim searchRange As Range
Dim search As String
Set searchRange = ThisWorkbook.Worksheets("Sheet1").Range("A1")
search = Left(searchRange.Value, 6)
Debug.Print search
End Sub
Here's a snippet to give you an idea of how you might go about solving the next step of the problem.
Sub Example2()
Dim compareRange As Range
Dim cell As Range
' SpecialCells is one of many ways to find all populated cells
Set compareRange = ThisWorkbook.Worksheets("Sheet1").Columns(2) _
.SpecialCells(xlCellTypeConstants)
For Each cell In compareRange
Debug.Print cell.Value
Next
End Sub
Please remember that StackOverflow is here to help with specific coding problems that you can't get over with the resources you can find online.

Answer 2

I had some difficulty deciphering exactly what you needed but here is what I have come up with.
I am going to assume that you know how to insert a module into your excel spreadsheet, copy code, and run a macro. If you do not know how please let me know and I will try to assist further.
If this is not what you need please provide me with a sample data set and the answers that you would like to get from the macro so that I can compare as I develop. Best of luck with your projects!
VBA module code
'This subroutine will take the contents of column A cells and search column B for matching digits
' if they are not found it will copy the current search term into column D
Option Explicit
Sub searchPrefix()
Dim cellContents As String
Dim tempSearchVariable As String
Dim isFound As Boolean
Dim quantitySearchCharacters As Integer
Dim entryCounter As Integer
Dim i As Integer
isFound = False
quantitySearchCharacters = 6
entryCounter = 0
'counts number of entries in column A
Cells.Range("A1").Select
Do Until IsEmpty(ActiveCell)
entryCounter = entryCounter + 1
ActiveCell.Offset(1, 0).Select
Loop
' gets value of comparison cell in column A
For i = 0 To entryCounter - 1
cellContents = Cells(1 + i, 1).Value
tempSearchVariable = Left(cellContents, quantitySearchCharacters)
Cells.Range("B1").Select
Do Until IsEmpty(ActiveCell)
' detects if B1 column cell content matches the current search terms and then adds more characters if required
If Left(ActiveCell.Value, quantitySearchCharacters) = tempSearchVariable Then
quantitySearchCharacters = quantitySearchCharacters + 1
tempSearchVariable = Left(cellContents, quantitySearchCharacters)
isFound = True
End If
If isFound Then
isFound = False 'reset flag
Cells.Range("B1").Select
Else
ActiveCell.Offset(1, 0).Select
End If
Loop
Cells(1 + i, 4).Value = tempSearchVariable ' prints the discovered unique prefix to column D
Next i
End Sub