Python - Sort Tuple List by Nth Element of Tuple

We are given list of tuple we need to sort tuple by Nth element of each tuple. For example d = [(1, 5), (3, 2), (2, 8), (4, 1)] and k=1 we need to sort by 1st element of each tuple so that output for given list should be [(4, 1), (3, 2), (1, 5), (2, 8)]

Using sorted() with lambda

sorted() function with a lambda key sorts a list of tuples based on Nth element by specifying lambda x: x[n]. It provides an efficient and concise way to perform element-wise tuple sorting

d = [(1, 5), (3, 2), (2, 8), (4, 1)]  
n = 1  
# Sort the list based on the Nth element using a lambda function
res = sorted(d, key=lambda x: x[n])

print(res) 

[(4, 1), (3, 2), (1, 5), (2, 8)]

Explanation:

• sorted() function sorts the list of tuples based on the nth element (index 1 in this case) using lambda x: x[n], meaning it sorts by second value in each tuple.
• Output will be [(4, 1), (3, 2), (1, 5), (2, 8)] as second elements [5, 2, 8, 1] are sorted in ascending order [1, 2, 5, 8].

Using operator.itemgetter()

operator.itemgetter(n) function retrieves the Nth element from each tuple allowing sorted() to sort list based on that element. It is more efficient than using a lambda function for tuple-based sorting.

from operator import itemgetter 

d = [(1, 5), (3, 2), (2, 8), (4, 1)] 
n = 1  
# Sort using itemgetter, which is optimized for retrieving elements by index
res = sorted(d, key=itemgetter(n))
print(res) 

[(4, 1), (3, 2), (1, 5), (2, 8)]

Explanation:

• itemgetter(n) function retrieves nth element from each tuple, allowing sorted() to arrange list based on that value.
• This method is more efficient than using a lambda function because itemgetter is implemented in C making it faster for large datasets.

Using pandas.DataFrame

A pandas.DataFrame allows storing list of tuples as a structured table and sorting it efficiently using .sort_values() method. This approach is useful for handling large datasets as Pandas provides optimized sorting and additional data manipulation features.

import pandas as pd  
d = [(1, 5), (3, 2), (2, 8), (4, 1)]

# Convert the list of tuples into a Pandas DataFrame
df = pd.DataFrame(d)

# Sort DataFrame by the second column (index 1) and convert back to list of tuples
res = df.sort_values(by=1).values.tolist()
print(res) 

[[4, 1], [3, 2], [1, 5], [2, 8]]

Explanation:

• List of tuples is converted into a Pandas DataFrame, where each tuple represents a row, making it easy to manipulate the data.
• sort_values(by=1) method sorts the DataFrame based on the second column (index 1), and .values.tolist() converts the sorted DataFrame back into a list of tuples.