Google spreadsheet: unique values query

[Anwen11]

Can anyone help me with this?
We collect data about students on a google spreadsheet. I need to filter for unique contacts ie those students who over the year of the spreadsheet were seen for the first time.

I need, for example, to find unique values (students) for classes, for seminars, for a club we run etc. I've searched for the information but I seem to be led to needing to create another column which isn't required - just unique numbers for these categories.

Many thanks.

So every student has a unique number, and you want to see their unique numbers depending which class etc. they are in.

Why not filter by the class/seminar/club, and then you'll see the student unique-identifier numbers for each one?

Thanks - sorry, I have a feeling that I wasn't very clear.

Say, I've had 100 students in seminars this year. There'll be quite a number among those 100 who have seen me in seminars more than once and some three or four times. I need to find out how many students, out of the 100, were unique contacts ie saw me (at least) once. Does this make sense.

Bill, Bill, Bill, Jane, Tom, Tom, Sally: here there would be 4 unique students.

Is there a formula for this?

Thanks!

Do need another column, i think, in excel or g-spreadsheets, read here.

I think it's a simple as using UNIQUE (A2:A100)

Many thanks lljkk and Abi - looking at the unique function guidance now and will also try using the formula Unique ..
Very grateful for your help.