Python – Find minimum k records from tuple list

Sometimes, while working with data, we can have a problem in which we have records and we require to find the lowest K scores from it. This kind of application is popular in web development domain. Let’s discuss certain ways in which this problem can be solved. 

Method #1 : Using sorted() + lambda The combination of above functionality can be used to perform this particular task. In this, we just employ sorted function, and print the lowest K elements using list slicing. 

Python3

# Python3 code to demonstrate working of
# Minimum K records
# Using sorted() + lambda

# Initializing list
test_list = [('Manjeet', 10), ('Akshat', 4), ('Akash', 2), ('Nikhil', 8)]

# Initializing K
K = 2

# printing original list
print("The original list is : " + str(test_list))

# Minimum K records
# Using sorted() + lambda
res = sorted(test_list, key = lambda x: x[1])[:K]

# printing result
print("The lowest K records are : " + str(res))

Output

The original list is : [('Manjeet', 10), ('Akshat', 4), ('Akash', 2), ('Nikhil', 8)]
The lowest K records are : [('Akash', 2), ('Akshat', 4)]

Method #2 : Using sorted() + itemgetter() The combination of above functions can also be used to perform this particular task. In this, the task performed by lambda function is performed by itemgetter() is used to get the index in tuple which has to be included in calculations. 

Python3

# Python3 code to demonstrate working of
# Minimum K records
# Using sorted() + itemgetter()
from operator import itemgetter

# Initializing list
test_list = [('Manjeet', 10), ('Akshat', 4), ('Akash', 2), ('Nikhil', 8)]

# Initializing K
K = 2

# printing original list
print("The original list is : " + str(test_list))

# Minimum K records
# Using sorted() + itemgetter()
res = sorted(test_list, key = itemgetter(1))[:K]

# printing result
print("The lowest K records are : " + str(res))

Output

The original list is : [('Manjeet', 10), ('Akshat', 4), ('Akash', 2), ('Nikhil', 8)]
The lowest K records are : [('Akash', 2), ('Akshat', 4)]

Method #3 : Using heapq.nsmallest()
This method uses the nsmallest() function from the heapq module which returns the k smallest elements from an iterable. This method is more efficient than sorting the entire list and slicing the first k elements as it only considers the k smallest elements and doesn’t sort the entire list.

Python3

# Python3 code to demonstrate working of
# Minimum K records
# Using heapq.nsmallest()
import heapq

# Initializing list
test_list = [('Manjeet', 10), ('Akshat', 4), ('Akash', 2), ('Nikhil', 8)]

# Initializing K
K = 2

# printing original list
print("The original list is : " + str(test_list))

# Minimum K records
# Using heapq.nsmallest()
res = heapq.nsmallest(K, test_list, key = lambda x: x[1])

# printing result
print("The lowest K records are : " + str(res))
#This code is contributed by Edula Vinay Kumar Reddy

Output

The original list is : [('Manjeet', 10), ('Akshat', 4), ('Akash', 2), ('Nikhil', 8)]
The lowest K records are : [('Akash', 2), ('Akshat', 4)]

Time complexity of using heapq.nsmallest() is O(nlogk) and the Auxiliary space is O(k).