Without sorting your column A values, it'll get tremendously complicated.

Here's what will work if they are sorted:

In cell B2 use the formula
=IF(COUNTIF($A$2:$A$28,A2)=1,"",1)

In cell B3 use this formula & copy it down
=IF(COUNTIF($A$2:$A$28,A3)=1,"",IF(COUNTIF(A$2:A3, A3)1,VLOOKUP(A3,A$2:B2,2,0),1+MAX(B$2:B2)))

"lehigh46" wrote:




In a privious post I asked the following question;

Column A has hundreds of item numbers.
Most are NOT duplicated, but I could have as many as 10 to 15 item
numbers with duplications and each number could be duplicated 3 to 10
times or more.

Question:

I need a formula for column B which will return a unique number for
each set of duplicates.


As it turns out I gave a poor example of what I needed.

************** Apoligies to Teethless mama ****************

The following is what I really need.


A B
1
2
3
4 1
4 1
4 1
5 2
5 2
6
7
27 5
9
10 3
10 3
10 3
4 1
10 3
10 3
10 3
10 3
24
25 4
25 4
26
27 5
5 2
27 5



Thanks for your help