Make a list of exact match duplicates in large spreadsheet

Originally Posted by martindwilson

what prefix do you want to add? it should be possible to do it all in one go with a formula, eg to add a,b,c....to front of those which are duplicates
something like
=IF(COUNTIF(A:A,A1)>1,CHAR(COUNTIF($A$1:A1,A1)+64)&TEXT(A1,"0"),TEXT(A1,"0"))

I'm not sure which prefix I'm going to use, my plan was to add a 2 or 3 letter prefix based on different vendors for the same part number.