Python Solutions to Find Students with the Second Lowest Grade

💡 Problem Formulation: We’re tasked with writing a Python program that processes a nested list where each inner list contains a student’s name and their grade. The goal is to find and display the names of all students with the second lowest grade. Given an input such as [["Harry", 37.21], ["Berry", 37.21], ["Tina", 37.2], ["Akriti", 41], ["Harsh", 39]], the program should output ["Harry", "Berry"] as they have the second lowest grade.

Method 1: Using List Comprehension and Sorting

This method involves sorting the nested list by grades, then using a list comprehension to filter out the names of students with the second lowest grade. This method is straightforward and easy to understand.

Here’s an example:

students = [["Harry", 37.21], ["Berry", 37.21], ["Tina", 37.2], ["Akriti", 41], ["Harsh", 39]]
students_sorted = sorted(students, key=lambda x: x[1])
second_lowest_grade = sorted(list(set([grade for name, grade in students_sorted])))[1]
second_lowest_students = [name for name, grade in students_sorted if grade == second_lowest_grade]
print(second_lowest_students)

Output:

['Harry', 'Berry']

This code snippet first sorts the list of students based on their grades. It then creates a set of unique grades, sorts them, and identifies the second lowest grade. Finally, it filters the students who have that grade and prints their names.

Method 2: Using a For Loop and Dictionary

Another way is to iterate over the list of students and store their names and grades in a dictionary. This method is good for handling larger data sets where look-up efficiency is important.

Here’s an example:

students = [["Harry", 37.21], ["Berry", 37.21], ["Tina", 37.2], ["Akriti", 41], ["Harsh", 39]]
grades = {}
for name, grade in students:
    if grade in grades:
        grades[grade].append(name)
    else:
        grades[grade] = [name]

second_lowest_grade = sorted(grades.keys())[1]
second_lowest_students = grades[second_lowest_grade]
print(second_lowest_students)

Output:

['Harry', 'Berry']

This code creates a dictionary where each grade points to a list of student names with that grade. It then retrieves and sorts the grades, identifying the second lowest where associated student names are printed.

Method 3: Using the heapq Module

The heapq module provides operations for min-oriented heaps, which can be used to efficiently find the second lowest grade without fully sorting the list.

Here’s an example:

import heapq

students = [["Harry", 37.21], ["Berry", 37.21], ["Tina", 37.2], ["Akriti", 41], ["Harsh", 39]]
grades = list(set([grade for name, grade in students]))
heapq.heapify(grades)
lowest_grade = heapq.heappop(grades)
second_lowest_grade = heapq.heappop(grades)
second_lowest_students = [name for name, grade in students if grade == second_lowest_grade]
print(second_lowest_students)

Output:

['Harry', 'Berry']

In this method, we convert our set of unique grades into a heap, from which the lowest and second lowest grades can be popped out. We then iterate through the original students list to print out the names of those with the second lowest grade.

Method 4: Avoiding Built-in Functions

For educational purposes or in restricted environments, you might need to find a solution without relying on Python’s built-in functions or modules. This requires a more manual approach to iterate through the list and determine the lowest and second-lowest grades.

Here’s an example:

students = [["Harry", 37.21], ["Berry", 37.21], ["Tina", 37.2], ["Akriti", 41], ["Harsh", 39]]
unique_grades = list({grade for _, grade in students})

lowest = second_lowest = float('inf')
for grade in unique_grades:
    if grade < lowest:
        second_lowest, lowest = lowest, grade
    elif grade < second_lowest:
        second_lowest = grade

second_lowest_students = [name for name, grade in students if grade == second_lowest]
print(second_lowest_students)

Output:

['Harry', 'Berry']

This method manually determines the lowest and second-lowest grades by iterating through the set of unique grades. Afterwards, it filters through the students to find those with the second lowest grade and prints their names.

Bonus One-Liner Method 5: Expressive Pythonic Approach

A one-liner approach can be utilized for impressing other developers with the compactness and expressiveness of Python syntax, although it can sometimes sacrifice readability.

Here’s an example:

students = [["Harry", 37.21], ["Berry", 37.21], ["Tina", 37.2], ["Akriti", 41], ["Harsh", 39]]
print([name for name, grade in sorted(students, key=lambda x: x[1])
      if grade == sorted({s[1] for s in students})[1]])

Output:

['Harry', 'Berry']

The one-liner Pythonic code sorts the students, creates a set of unique grades, sorts it, then iterates through the students to output those with the second lowest grade—all in one comprehensive line of code.

Summary/Discussion

• Method 1: List Comprehension and Sorting. Strengths: Simple and concise. Weaknesses: Not the most efficient for large data sets.
• Method 2: Dictionary and Loops. Strengths: Efficient for larger datasets. Weaknesses: Slightly more complex code.
• Method 3: heapq Module. Strengths: Efficient approach to finding the lowest elements without full sort. Weaknesses: Requires understanding of the heapq module.
• Method 4: Avoiding Built-ins. Strengths: Educational, doesn’t rely on Python’s built-ins. Weaknesses: More verbose, less idiomatic Python.
• Method 5: One-liner. Strengths: Compact and demonstrates Python capabilities. Weaknesses: Could be difficult to read and understand, especially for beginners.