Create 1-col array identifying occurrence count in a 1-col array

Given a column array {a;b;a;c;a;d;b} I need a formula to give the result {1;1;2;1;3;1;2}
I do not want to use a helper column.

If the array occupies (A1:A7) the required result can be obtained in C1 to C7 by dragging
=COUNTIF($A$1:A1,"="&A1)
down from C1 to C7. But I want the result to be an array.

The formula {=COUNTIF($A$1:$A$7,"="&$A$1:$A$7)} creates {$B$1:$B$7} as {3;2;3;1;3;1;2}

I am trying to create arrays in cols. B and C which look like:
a 3 1
b 2 1
a 3 2
c 1 1
a 3 3
d 1 1
b 2 2

Does anyone know any clever tricks using INDEX, MATCH, COUNTIF, SMALL for example which might achieve this?
Any suggestions would be appreciated, especially if they do not involve VBA

Something like this, entered as an array formula in cells B1:B7 seems to work for me:

=COUNTIF(A1:OFFSET(A1,ROW(A1:A7)-1,0),A1:A7)

Brilliant. Many Thanks! The OFFSET function is the key, and it hasn't been in my vocabulary.