Python – Nearest K Sort

Given a List of elements, perform sort on basis of its distance from K.

Input : test_list = [6, 7, 4, 11, 17, 8, 3], K = 10 
Output : [11, 8, 7, 6, 4, 17, 3] 
Explanation : 11-10 = 1; < 10 – 8 = 2 .. Ordered by increasing difference.

Input : test_list = [6, 7, 4, 11], K = 10 
Output : [11, 7, 6, 4] 
Explanation : 11-10 = 1; < 10 – 7 = 3 .. Ordered by increasing difference. 

Method #1 : Using sort() + abs()

In this, we perform sorting using sort() and abs() is used to get the difference, used for logic formation to perform sort operation upon.

Python3

# Python3 code to demonstrate working of
# Nearest K Sort
# Using sort() + abs()

# getting absolute difference
def get_diff(ele):

    # returning absolute difference
    return abs(ele - K)


# initializing list
test_list = [6, 7, 4, 11, 17, 8, 3]

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

# initializing K
K = 10

# performing inplace sort using sort()
test_list.sort(key=get_diff)

# printing result
print("Sorted List : " + str(test_list))

Output

The original list is : [6, 7, 4, 11, 17, 8, 3]
Sorted List : [11, 8, 7, 6, 4, 17, 3]

Time Complexity: O(n*nlogn) where n is the number of elements in the list “test_list”.  sort() + abs() performs n*nlogn number of operations.
Auxiliary Space: O(n), extra space is required where n is the number of elements in the list

Method #2 : Using sorted() + lambda + abs()

Similar to above method, here, sorted() is used to perform sort operation and rather than calling external function, lambda is used to provide sorting logic.

Python3

# Python3 code to demonstrate working of
# Nearest K Sort
# Using sorted() + abs() + lambda

# initializing list
test_list = [6, 7, 4, 11, 17, 8, 3]

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

# initializing K
K = 10

# sorted() used to perform sorting, lambda function to get logic
res = sorted(test_list, key=lambda ele: abs(ele - K))

# printing result
print("Sorted List : " + str(res))

Output

The original list is : [6, 7, 4, 11, 17, 8, 3]
Sorted List : [11, 8, 7, 6, 4, 17, 3]

Method #3: Using heapq.nsmallest()

Import the heapq module.
Initialize an empty list to store the absolute difference between each element of the given list and the given value of K.
Use a for loop to iterate through the given list.
Calculate the absolute difference between the current element and the given value of K using the abs() function, and append it to the list initialized in step 2.
Use the heapq.nsmallest() function to find the K nearest elements to the given value of K. This function returns a list of the K smallest elements from the given list in ascending order.
Print the resulting list.

Python3

import heapq

test_list = [6, 7, 4, 11, 17, 8, 3]
K = 10

# Initialize an empty list to store the absolute difference
abs_diff = []

# Calculate the absolute difference between each element and K
for num in test_list:
    abs_diff.append(abs(num - K))

# Use heapq.nsmallest() to find the K nearest elements
res = heapq.nsmallest(K, test_list, key=lambda x: abs(x - K))

print("Nearest K elements to", K, ":", res)

Output

Nearest K elements to 10 : [11, 8, 7, 6, 4, 17, 3]

Time complexity: O(n log K) where n is the length of the given list and K is the number of elements to be returned.
Auxiliary space: O(n) for storing the absolute difference between each element and the given value of K.