How can I sum each list within a nested list using a Python function?

Question

I have a random set of test scores for 50 students. Each student answered 20 questions, and the maximum score for each question is 5. How can I get the total score of each student in a list by using a Python function?

results_sheet = []
num_of_questions = 20
num_students = 50


#generate scores for each student and append to results_sheet

for student in range(num_students):
        scores = random.choices(list(range(0,6)),k=num_of_questions)
        results_sheet.append(scores)
        
#The result here is a list of lists.

So if I call the results for 2 students, I will get the following:

print(results_sheet[0:2])
[[4, 2, 3, 4, 2, 0, 0, 1, 2, 4, 0, 3, 5, 4, 3, 2, 5, 0, 3, 3], [5, 1, 1, 3, 2, 0, 2, 5, 3, 1, 1, 3, 5, 1, 4, 3, 2, 4, 5, 4]]

I have tried the following code but am missing something. Or perhaps the code is simply wrong:

def sum_score(results_sheet):

total = 0
for val in results_sheet:
    total = total + val
return total

The end result should look something like this for 2 students:

total_scores = [47, 55]

Are you resetting the results_sheet between each loop iteration? — Zaid Al Shattle
– Zaid Al Shattle, Commented Jul 21, 2021 at 8:32
What that piece of code you provided returns. Because i'm not sure how the result_sheet looks like. Is it 2D list looking like result_sheet[num_students][num_of_questions] — Piotr Nowakowski
– Piotr Nowakowski, Commented Jul 21, 2021 at 8:34

mgaliazzi · Accepted Answer · 2021-07-21 09:44:06Z

2

You can easily use numpy.sum, and set axis to negative.

import random
import numpy

results_sheet = []
num_of_questions = 20
num_students = 50


#generate scores for each student and append to results_sheet

for student in range(num_students):
        scores = random.choices(list(range(0,6)),k=num_of_questions)
        results_sheet.append(scores)

If you want the sum of all:

numpy.sum(results_sheet, axis=-1)

array([43, 44, 61, 64, 52, 44, 48, 51, 36, 50, 51, 45, 56, 47, 53, 60, 53,
       45, 45, 46, 53, 54, 39, 42, 54, 67, 44, 48, 51, 58, 53, 54, 40, 52,
       62, 54, 61, 58, 47, 38, 51, 45, 50, 49, 61, 30, 50, 59, 54, 34])

So if I call the results for 2 students:

numpy.sum(results_sheet, axis=-1)[0:2]
array([43, 44])

edited Jul 21, 2021 at 9:44

answered Jul 21, 2021 at 9:08

mgaliazzi

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1 Comment

mgaliazzi Over a year ago

You are welcome. you can also use the following setting, numpy.sum(results_sheet[A:B], axis=0)[X:Y] to know the result of students between A and B on the X:Y questions.

U13-Forward · Accepted Answer · 2021-07-21 08:59:40Z

1

Try a list comprehension:

final = [sum(lst) for lst in results_sheet]

Or use map:

final = list(map(sum, results_sheet))

Edit:

To use a function:

def func(results_sheet):
    return [sum(lst) for lst in results_sheet]
print(func(results_sheet))

edited Jul 21, 2021 at 8:59

answered Jul 21, 2021 at 8:36

U13-Forward

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3 Comments

CTan Over a year ago

Thank you, @U11-Forward. Both solutions were helpful. What if I wanted to use a function to solve the problem?

U13-Forward Over a year ago

@CTan Check my Edit: part, please accept and upvote if it helps

U13-Forward Over a year ago

@CTan I did the function in the recent edit

mabergerx · Accepted Answer · 2021-07-21 08:34:15Z

1

First, if you are having a return statement outside of a function it will not work. Secondly, you can also just use the build-in sum function in Python:

sum_of_all = sum(scores)

Then you can do this for each individual student's scores:

results_sheet = []
num_of_questions = 20
num_students = 50


#generate scores for each student and append to results_sheet

for student in range(num_students):
        scores = random.choices(list(range(0,6)),k=num_of_questions)
        results_sheet.append(scores)

sums = [sum(result_sheet) for result_sheet in results_sheet]

The sums variable will be a list of summed scores for the students, in the same order as the generated scores.

answered Jul 21, 2021 at 8:34

mabergerx

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Comments

Marcel Preda · Accepted Answer · 2021-07-21 08:37:42Z

1

You have to apply sum() on every 2nd level list, like below

import random

results_sheet = []
num_of_questions = 20
num_students = 50


#generate scores for each student and append to results_sheet

for student in range(num_students):
        scores = random.choices(list(range(0,6)),k=num_of_questions)
        results_sheet.append(scores)


total = 0
for val in results_sheet:
    total = total + sum(val)
print(total)

answered Jul 21, 2021 at 8:37

Marcel Preda

1,2157 silver badges20 bronze badges

2 Comments

Marcel Preda Over a year ago

Actually you don't need the second for loop, you can do the sum in the first loop total = total + sum(scores), the code will be faster. Of course you have to set total = 0 before the 1st loop.

CTan Over a year ago

Thank you, that helps in getting the total score for all students.

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