Counting number of occurrences in column?

Question

What would be a good approach to calculate the number of occurrences in a spreadsheet column? Can this be done with a single array formula?

Example (column

Answer 1

A simpler approach to this

At the beginning of column B, type

=UNIQUE(A:A)

Then in column C, use

=COUNTIF(A:A, B1)

and copy them in all row column C.

Edit: If that doesn't work for you, try using semicolon instead of comma:

=COUNTIF(A:A; B1)