IF Statement that Counts

I am trying to accomplish the following. I have a list of data that contains headers and some unique fields. See the attachment for the example.

In short, I need the KEY column to count, starting from 1, however, on rows that have a matching Document Number, it uses the same KEY value and then continues on counting where it left off.

I am trying to figure out the best way to do this and while I could make a super long IF statement, I feel like there is a better way.

Hi mehmetcik,

This is nearly exactly what I was looking for. I appreciate the time taken for this.

It works in my uploaded test Excel file, but not so much in actual practice with the real document. There are a few headers that I left out in the example document, because (so I thought) they aren't applicable to the example. In the live document that I am using, DOCNMBR will be column G (7). Therefore, should I adjust

Please Login or Register  to view this content.

To look like this below?

Please Login or Register  to view this content.

Another comment to make is the live document I am using uses formulas everywhere. Meaning, DOCNMBR isn't a plain text of '123456' and its =IF($H2<>"",'Pay Entry'!B14,""). Would this code provided still function even if the cells are formulas?

If desired, I can upload a more accurate copy of my live/real Excel file. I figured a formula was going to be provided, not code, hence the reason for not uploading the full document.

A formula method..

enter the first number by hand in L2..
So L2 = 1

IN L3 and filled down
=IF(COUNTIF(K$2:K3,K3)>1,VLOOKUP(K3,K$2:L3,2,0),MAX(L$2:L2)+1)

Worked like a charm in both cases! Thank you!