Aggregating data from multiple lists via list comprehension

Question

I'm writing the following code to calculate consolidated grades of student to manage their Transcript, but not getting desired output, could someone help me in this,Thanx!

def transcript(coursedetails, studentdetails, grades):
    studentdetails.sort()
    coursedetails.sort()
    grades.sort()
    result=[(student,grade,coursedetail)
            for student in studentdetails 
            for grade in grades for coursedetail in coursedetails 
            if((student[0]==grade[0])and(grade[1]==coursedetail[0]))]
    print(result)

Input I'm giving is---

transcript([("MA101","Calculus"),("PH101","Mechanics"),("HU101","English")],[("UGM2018001","Rohit Grewal"),("UGP2018132","Neha Talwar")],[("UGM2018001","MA101","AB"),("UGP2018132","PH101","B"),("UGM2018001","PH101","B")])

Actual Output---

[(('UGM2018001', 'Rohit Grewal'), ('UGM2018001', 'MA101', 'AB'), ('MA101', 'Calculus')), (('UGM2018001', 'Rohit Grewal'), ('UGM2018001', 'PH101', 'B'), ('PH101', 'Mechanics')), (('UGP2018132', 'Neha Talwar'), ('UGP2018132', 'PH101', 'B'), ('PH101', 'Mechanics'))]

Desired Output---

[('UGM2018001', 'Rohit Grewal', [('MA101', 'Calculus', 'AB'), ('PH101', 'Mechanics', 'B')]), ('UGP2018132', 'Neha Talwar', [('PH101', 'Mechanics', 'B')])]

You just asked that question and we told you it was a duplicate — Olivier Melançon, Mar 10 '18 at 15:20
Possible duplicate of ["Least Astonishment" and the Mutable Default Argument](https://stackoverflow.com/questions/1132941/least-astonishment-and-the-mutable-default-argument) — Anton Kazakov, Mar 10 '18 at 16:25
I've looked over this question and I don't see resemblance to the question mentioned in the previous comment. There are not even any Default Arguments passed. — Mike Peder, Mar 11 '18 at 02:16

score 0 · Answer 1 · answered Mar 11 '18 at 02:12

You may consider changing your structure from a list of tuples to a dictionary as it will be much easier to manipulate the information.

def transcript(coursedetails, studentdetails, grades):
    result = {}
    students = {}
    courses = {}
    for course, descript in coursedetails:
        courses[course] = descript
    for sid, student in studentdetails:
        students[sid] = {'name':student}
    for sid, course, grade in grades:
        details = (course, courses[course], grade)
        if not 'grades' in students[sid]:
            students[sid]['grades'] = []
        students[sid]['grades'].append(details)
    return  students

This returns a dictionary of dictionaries for your transcript where the student ids are the keys that return a dictionary holding your student's name and grades.

Test:

trans = transcript([("MA101","Calculus"),("PH101","Mechanics"),("HU101","English")],[("UGM2018001","Rohit Grewal"),("UGP2018132","Neha Talwar")],[("UGM2018001","MA101","AB"),("UGP2018132","PH101","B"),("UGM2018001","PH101","B")])

Result:

{'UGM2018001': {'name': 'Rohit Grewal', 'grades': [('MA101', 'Calculus', 'AB'), ('PH101', 'Mechanics', 'B')]}, 'UGP2018132': {'name': 'Neha Talwar', 'grades': [('PH101', 'Mechanics', 'B')]}}

If you still want this information in the Desired Output described above, then the following will create a list of tuples exactly as you needed.

list((k,v['name'], v['grades']) for k,v in trans.items())

jpp · Answer 2 · 2018-03-11T04:19:47.313

This is possible with collections.defaultdict:

from collections import defaultdict

inputs = [("MA101","Calculus"),("PH101","Mechanics"),("HU101","English")],\
         [("UGM2018001","Rohit Grewal"),("UGP2018132","Neha Talwar")],\
         [("UGM2018001","MA101","AB"),("UGP2018132","PH101","B"),("UGM2018001","PH101","B")]

def transcript(coursedetails, studentdetails, grades):

    d = defaultdict(list)

    courses, students = dict(coursedetails), dict(studentdetails)

    for grade in grades:
        d[(grade[0], students[grade[0]])].append((grade[1], courses[grade[1]], grade[2]))

    return d

res = transcript(*inputs)

Result

defaultdict(list,
            {('UGM2018001', 'Rohit Grewal'): [('MA101', 'Calculus', 'AB'),
                                              ('PH101', 'Mechanics', 'B')],
             ('UGP2018132', 'Neha Talwar'): [('PH101', 'Mechanics', 'B')]})

If you really need a list of tuples, this is easy to transform:

res2 = [(k[0], k[1], v) for k, v in res.items()]

# [('UGM2018001', 'Rohit Grewal', [('MA101', 'Calculus', 'AB'),
#                                  ('PH101', 'Mechanics', 'B')]),
#  ('UGP2018132', 'Neha Talwar', [('PH101', 'Mechanics', 'B')])]

Aggregating data from multiple lists via list comprehension

2 Answers2