IndexError: list index out of range when in python, even when the range exists

Question

I am sure that the range which I am trying to access exists, but still, the program shows error. I am trying to make a program which will sum up the values in a column corresponding to the values in the other column.

for example:

   28400    4
   28400    34 
   28400    9
   65478    2
   65478    5
   65478    3

what my program will do is, it will add up 4,34 and 9 and then it will add up 2,5 and 3 and then following will be the output-

   47
   47
   47
   10
   10
   10  

I am importing data from a CSV file. following is the code-

    import pandas as pd
    import numpy as np

    assessment = pd.read_csv('/home/user/Documents/MOOC dataset original/studentVle2.csv')


    assessment = assessment.values

    count=0
    stucount=28400
    sumc=[]
    i=0
    for stu in assessment[:,2:3]:
        if(stucount==stu):
            count = count + assessment[i,5]
            i=i+1
        else:
            sumc.append(count)
            count = 0
            count = count + assessment[i,5]
            i=i+1
        stucount=stu

    #print(sumc)

    stucount=28400
    i=0
    a=[]
    for stu in assessment[:,2:3]:
        if(stucount==stu):
            a.append(sumc[i])
            stucount = stu
        else:
            i=i+1
            a.append(sumc[i])
            stucount = stu

    print(a)

Error:

        File "/home/user/Documents/final project files/test.py", line 36, in <module>
        a.append(sumc[i])
        IndexError: list index out of range

and by the way, before adding some lines, like i=i+1,stucount=stu this error was not shown, but now it shows even though what happening is the same.

Answer 1

The error is because you are not adding assessment value to sumc list for the last student after the loop ends. So, for n unique student id, the list length is only n-1. After for loop, add sumc.append(count). See below.

assessment = assessment.values

count=0
stucount=28400
sumc=[]
i=0
for stu in assessment[:,2:3]:
    if(stucount==stu):
        count = count + assessment[i,5]
        i=i+1
    else:
        sumc.append(count)
        count = 0
        count = count + assessment[i,5]
        i=i+1
    stucount=stu

sumc.append(count)
print(sumc)

stucount=28400
i=0
a=[]
for stu in assessment[:,2:3]:
    if(stucount==stu):
        a.append(sumc[i])
        stucount = stu
    else:
        a.append(sumc[i])
        stucount = stu
        i=i+1

print(a)

Answer 2

Here, i'm just going by your initial problem statement of what you have and what you want to get.

df = pd.DataFrame([[28400,4],
                   [28400,34],
                   [28400,9],
                   [65478,2],
                   [65478,5],
                   [65478,3]], columns=list('AB'))
sums = df.groupby('A').B.sum()
df.A.map(sums)

And you get

0    47
1    47
2    47
3    10
4    10
5    10
Name: A, dtype: int64

Was this what you were looking for?

Answer 3

Place i=i+1 below stucount = stu and then try

import pandas as pd
import numpy as np

assessment = pd.read_csv('/home/user/Documents/MOOC dataset original/studentVle2.csv')


assessment = assessment.values

count=0
stucount=28400
sumc=[]
i=0
for stu in assessment[:,2:3]:
    if(stucount==stu):
        count = count + assessment[i,5]
        i=i+1
    else:
        sumc.append(count)
        count = 0
        count = count + assessment[i,5]
        i=i+1
    stucount=stu

#print(sumc)

stucount=28400
i=0
a=[]
for stu in assessment[:,2:3]:
    if(stucount==stu):
        a.append(sumc[i])
        stucount = stu
    else:
        a.append(sumc[i])
        stucount = stu
        i=i+1

print(a)

The output will be different and change accordingly....error will be removed

Answer 4

I think you should add i=i+1 after the error line a.append(sumc[i]). Because in your code, may out of range of list at last.