Hello Nathalie,

I suggest to select a sufficiently long range with two columns and to
array-enter:
=Pfreq(A1:A999,B1:B999)
[Enter with CTRL + SHIFT + ENTER, not only with ENTER.]

Pfreq is a user-defined function:
http://sulprobil.com/html/pfreq.html

Press ALT + F11, enter a new module, copy my function (macro text)
into the new module, go back to your worksheet and the formula
mentioned above will work.

Regards,
Bernd