Numbering Duplicates

[Edgar Thoemmes]

Hi,

Could someone help me with a formula for the following?

I have a list of data which I would like to highlight the duplicates in.
Basically I would like to add a column which would prefix the value by a
number which would increase by each duplicate

AAAA
AAAA
AABA
AABA
AACA
AADA

Would become

1_AAAA
2_AAAA
1_AABA
2_AABA
1_AACA
1_AADA

Etc etc.....Can anyone help?

Thanks

 

[Ardus Petus]

in B1, enter:
=COUNTIF($A$1:$A1,A1)&"_"&A1
and copy down


HTH