The data contain several unique classes "class_id" (byte, values 1-20) with students "student_id" (byte, values 1-30, 1-29, 1-24, etc.).

Resp1 - Resp3 contain byte values of student_id.

Here is a snapshot of the data.
class_id student_id Resp1 Resp2 Resp3
1 1 9 7 5
1 2 14 4 22
1 3 1 . 22
1 28 30 1 1
1 29 2 22 4
1 30 9 . 18
2 1 3 15 13
2 2 17 25 1
2 3 3 17 9
I would like to count the frequency each student_id across observations of Resp1-Resp3 within each class_id.
My goal in using tabcount is to eventually create a variable that contains frequency of student_id for each observation of a student_id in a class_id.

Essentially, this command below, but across all Resp variables, with student_ids with zero occurrences included, missing excluded from display.
bysort student_id (class_id): tab PN1, matcell(matrix`Class')
svmat matrix`Class'

My thought is tabcount should be able to handle this. But when I run the following, I receive a type mismatch r(109) error. None of the variables are string. Could it be I'm misusing a macro? (I also don't quite understand how what arguments c() or v() are supposed to take.)

vl create Resp_list = (Resp1 Resp2 Resp3)
foreach var in $Resp_list{
di "Var is: `var'"
bysort class_id (student_id): tabcount `var', c(`var') zero
}

Any help is appreciated!