If you don't want users to.
How to create drop down list in excel without duplicates. Unique + sort function in excel formula Web download the featured file here: Excel drop down lists are intuitive.
Select the range of cells, click copy to another location,. Web totero's answer is correct. How to create multiple drop down lists in excel without repetition.
In the data validation dialog. The link is also very helpful. Basically the formula you need is:
B2=index ($a$2:$a$20, match (0, countif ($b$1:b1, $a$2:$a$20), 0)). Web on the data tab, in the sort & filter group, click advanced. Select the table, click insert > pivottable, then choose a position for.