Rank a list of students based on marks using python list comprehension

Here, we are going to rank a list of students in a cleaner way without using any loops. This is achieved using python List comprehension. We have a list of students with id, name and marks in 3 different subjects.

Normally, to rank a list, we will have to loop through the list to find the total marks of each student. Then we will have to sort and find the ranks. We can do all these in just 3 lines, if we use List comprehension. Refer sample below.

Here we are using the python walrus operator to find the rank in the final step.
s := s + 1
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studentsList = [ [1, 'Carl', 48, 47, 45 ], [2, 'Tim', 43, 42, 41 ], [3, 'Peter', 40, 44, 47 ], [4, 'George', 44, 49, 50 ], [5, 'Kim', 41, 41, 42 ] ] #Find Total listToRank = [ [ st[0], st[1], st[2]+st[3]+st[4] ] for st in studentsList] #Order by using marks listToRank.sort(key=lambda x: x[2], reverse=True) #Rank s = 0 rankedList = [ [ st[0], st[1], st[2], s := s + 1 ] for st in listToRank] print(rankedList)
Output:
```
[
	[4, 'George', 143, 1],
	[1, 'Carl', 140, 2],
	[3, 'Peter', 131, 3],
	[2, 'Tim', 126, 4],
	[5, 'Kim', 124, 5]
]
```

If input data is in key-value pairs

The list has data in the form of key-value pairs.
We are going to update values of the already existing key named "rank".
This is done using a python library named operator.
Call operator.setitem() with 3 parameters, list item, key name and the new value.

import operator

studentsList = [
    {'id': 1, 'name': 'Carl', 'english': 48, 'science': 47, 'maths': 45, 'total': 0, 'rank': 0 },
    {'id': 2, 'name': 'Tim', 'english': 43, 'science': 42, 'maths': 41, 'total': 0, 'rank': 0 },
    {'id': 3, 'name': 'Peter', 'english': 40, 'science': 44, 'maths': 47, 'total': 0, 'rank': 0 },
    {'id': 4, 'name': 'George', 'english': 44, 'science': 49, 'maths': 50, 'total': 0, 'rank': 0 },
    {'id': 5, 'name': 'Kim', 'english': 41, 'science': 41, 'maths': 42, 'total': 0, 'rank': 0 }
]

#Find Total
[operator.setitem(st, "total", st["english"] + st["science"] + st["maths"]) for st in studentsList]

#Order by using marks
studentsList.sort(key=lambda x: x['total'], reverse=True)

#Rank
s = 0
[operator.setitem(st, "rank", s := s + 1 ) for st in studentsList]
print(studentsList)

Output:

[
	{'id': 4, 'name': 'George', 'english': 44, 'science': 49, 'maths': 50, 'total': 143, 'rank': 1},
	{'id': 1, 'name': 'Carl', 'english': 48, 'science': 47, 'maths': 45, 'total': 140, 'rank': 2},
	{'id': 3, 'name': 'Peter', 'english': 40, 'science': 44, 'maths': 47, 'total': 131, 'rank': 3},
	{'id': 2, 'name': 'Tim', 'english': 43, 'science': 42, 'maths': 41, 'total': 126, 'rank': 4},
	{'id': 5, 'name': 'Kim', 'english': 41, 'science': 41, 'maths': 42, 'total': 124, 'rank': 5}
]