UNIQUE formula in Google Sheets for multiple ranges

Question

I have a list of participants in column A. A full employee list in column B. I want to get the list of non-participants in column C. Basically 'BA' but in list form.

'January' is the participants list:

Answer 1

try:

=FILTER(A:A; NOT(COUNTIF(B:B; A:A)))

Answer 2

It is always an added challenge to write formulas when we don't have access to actual date. But based on what I can see, try this formula in the top cell of any empty column:

=ArrayFormula({"My Header"; FILTER(R2:R,ISERROR(VLOOKUP(TRIM(R2:R),TRIM(T2:T),1,FALSE)))})

You can change "My Header" to something meaningful.

The next part means "FILTER in anything in the range R2:R that cannot be found [ie, ISERROR(VLOOKUP(...)) ] in T2:T."

TRIM is used just to account for any accidental/stray spaces that may occur in either list, since that would result in no match if one or the other had extra space.

If this does not do what you expect, please share a link to a sample spreadsheet.