How to count number of individual values?

[mattisipola]

I want to count how many times the same value appears in a table column (Stamp Date) for the same person. Individual values ​​have been calculated manually. What would be a good way to implement this with formulas?

Thank you.

[#2]

@mattisipola 

In D2:

=IF(A2=A3, "", COUNT(UNIQUE(FILTER($B$2:$B$27, $A$2:$A$27=A2))))

Fill down.

[#3]

@HansVogelaar It's not work

What I did wrong?

[#4]

@mattisipola 

Do you use comma as decimal separator? If so, change all commas in the formula to semicolons i.e. ;