dc.js reductio error. I need to get unique counts of items that are repeated (and dependent) on other items

Question

In my project, the data looks like

teacher,total_students,date,activity_type,activity_subject,project_id,teacher_id,student,submission_date,n_of_words,vocabulary_used,section_number,student_grade,grading_rubric,grading_score
    Jennifer,19,03/01/2020,Journal,Social Studies,152,4,Josh,03/01/2020,23,2,2,2,Explanatory,3.5
    Jennifer,19,03/01/2020,Journal,Social Studies,152,4,Maria,03/01/2020,254,1,2,5,Explanatory,1.5
    Jennifer,19,03/01/2020,Journal,Social Studies,152,4,Mark,03/01/2020,304,4,2,5,Explanatory,1.5
    Jennifer,19,03/01/2020,Journal,Social Studies,152,4,Brianna,03/01/2020,38,4,2,4,Explanatory,2.7
    Jennifer,19,03/01/2020,Journal,Social Studies,152,4,Bobbie,03/01/2020,151,3,2,6,Explanatory,3.9
    Jennifer,19,03/01/2020,Journal,Social Studies,152,4,Hannah,03/01/2020,207,4,2,6,Explanatory,3.5
    Jennifer,19,03/01/2020,Journal,Social Studies,152,4,Jodie,03/01/2020,209,2,2,4,Explanatory,3.5
    Jennifer,19,03/01/2020,Journal,Social Studies,152,4,Luis,03/01/2020,57,3,2,5,Explanatory,1.5
    Jennifer,19,03/01/2020,Journal,Social Studies,152,4,George,03/01/2020,99,3,2,5,Explanatory,3.5
    Jennifer,19,03/01/2020,Journal,Social Studies,152,4,Alice,03/01/2020,106,4,2,4,Explanatory,3.2
    Jennifer,19,03/01/2020,Journal,Social Studies,152,4,Alex,03/01/2020,300,1,2,6,Explanatory,3
    Jennifer,19,03/01/2020,Journal,Social Studies,152,4,Andrew,03/01/2020,155,3,2,5,Explanatory,1.5
    Jennifer,19,03/01/2020,Journal,Social Studies,152,4,Amber,03/01/2020,305,4,2,2,Explanatory,3.7
    Jennifer,19,03/01/2020,Journal,Social Studies,152,4,Bobby,03/01/2020,97,3,2,3,Explanatory,2
    Jennifer,19,03/01/2020,Journal,Social Studies,152,4,Bonnie,03/01/2020,175,1,2,4,Explanatory,2.5
    Jennifer,19,03/01/2020,Journal,Social Studies,152,4,Brandy,03/01/2020,85,2,2,5,Explanatory,2.7
    Jennifer,19,03/01/2020,Journal,Social Studies,152,4,Bruce,03/01/2020,263,3,2,5,Explanatory,4
    Jennifer,19,03/01/2020,Journal,Social Studies,152,4,Cristopher,03/01/2020,123,4,2,2,Explanatory,3.2
    Jennifer,19,03/01/2020,Journal,Social Studies,152,4,Caleb,03/01/2020,98,4,2,2,Explanatory,3.9
    Megan,2,03/01/2020,Story,Social Studies,287,8,George,03/01/2020,125,1,1,2,Explanatory,2
    Megan,2,03/01/2020,Story,Social Studies,287,8,Alice,03/01/2020,280,3,1,5,Explanatory,1.5
    Josh,1,03/01/2020,Journal,Science,986,2,Sean,03/01/2020,327,1,1,5,Explanatory,1.5
    Laura,4,03/01/2020,Journal,Social Studies,441,6,Larry,03/01/2020,173,4,3,4,Explanatory,4
    Laura,4,03/01/2020,Journal,Social Studies,441,6,Sean,03/01/2020,257,4,3,5,Explanatory,4
    Laura,4,03/01/2020,Journal,Social Studies,441,6,Tom,03/01/2020,124,6,3,4,Explanatory,3.5
    Laura,4,03/01/2020,Journal,Social Studies,441,6,Noah,03/01/2020,41,6,3,6,Explanatory,3.9
    Jan,19,03/01/2020,Assignment,Science,890,3,Eric,03/01/2020,182,1,3,6,Explanatory,2
    Jan,19,03/01/2020,Assignment,Science,890,3,Ethan,03/01/2020,251,1,3,6,Explanatory,3.9
    Jan,19,03/01/2020,Assignment,Science,890,3,Evan,03/01/2020,305,3,3,4,Explanatory,2.5

Each teacher can have several project_ids, but the same project_id is can be repeated in the rows for different students.

I need to be able to get the unique count of the project_ids. I am trying to use Reductio for this. I am doing:

const myChart = dc.numberDisplay(divRef);

const projectDimension =  ndx.dimension(function (d) {
    return d.project_id;
});

const teachers = ndx.dimension(function (d) {
  return d.teachers;
});

const teachersGroup = teachers.group();
const reducer = reductio()
  .exception(function(d) { return d.project_id; })
  .exceptionCount(true)(teachersGroup) 
  
//teachersGroup.top(Infinity);  
console.log(teachersGroup.top(Infinity))

But, I get this error:

quicksort.js:142 Uncaught RangeError: Maximum call stack size exceeded

What I am doing wrong?