find-student-course-pairs.js

const _ = require('underscore');

const studentCoursePairs1 = [
  ['58', 'Linear Algebra'],
  ['94', 'Art History'],
  ['94', 'Operating Systems'],
  ['17', 'Software Design'],
  ['58', 'Mechanics'],
  ['58', 'Economics'],
  ['17', 'Linear Algebra'],
  ['17', 'Political Science'],
  ['94', 'Economics'],
  ['25', 'Economics'],
  ['58', 'Software Design'],
];

function findPairs(pairs) {
  const studentMap = pairs.reduce((acc, [id, course]) => {
    acc[id] = (acc[id] ?? []).concat(course);
    return acc;
  }, {});

  // 2D map of students
  const studentPairs = pairs
    // Get IDs
    .map(pair => pair[0])
    // Get unique IDs
    .reduce((acc, id) => (acc.includes(id) ? acc : acc.concat(id)), [])
    // New struct with pairs and shared classes (empty for now)
    .reduce((acc, id, i, ids) => {
      acc[id] = ids.filter(_id => _id !== id).reduce((_acc, _id) => {
        // eslint-disable-next-line no-param-reassign,no-underscore-dangle
        _acc[_id] = _.intersection(studentMap[id], studentMap[_id]);
        return _acc;
      }, {});
      return acc;
    }, {});

  function genKey(id1, id2) {
    return [id1, id2].sort().join(',');
  }

  return Object.entries(studentPairs).reduce((acc, [id1, subMap]) => {
    return Object.entries(subMap).reduce((acc2, [id2, courses]) => {
      if (acc[genKey(id1, id2)]) return acc;

      acc[genKey(id1, id2)] = courses;
      return acc;
    }, {});
  }, {});
}

console.log(findPairs(studentCoursePairs1));