Creating a Sorted Merged List of Two Unsorted Lists in Python

Creating a Sorted Merged List of Two Unsorted Lists in Python

Last Updated : 17 Jan, 2025

Creating a sorted merged list of two unsorted lists involves combining the elements of both lists and sorting the resulting list in ascending order.

For example: If we have list1 = [25, 18, 9] and list2 = [45, 3, 32] the output will be [3, 9, 18, 25, 32, 45].

Using `+` Operator

This method merges the two lists using the + operator which concatenates them and then combined list is sorted using the sort() method.

a = [25, 18, 9, 41, 26, 31]
b = [25, 45, 3, 32, 15, 20]

# Merge and sort using + operator and sort()
res = a + b
res.sort()    

print(res)

 
a = [25, 18, 9, 41, 26, 31]
b = [25, 45, 3, 32, 15, 20]​# Merge and sort using + operator and sort()res = a + bres.sort()    ​print(res)

Output

[3, 9, 15, 18, 20, 25, 25, 26, 31, 32, 41, 45]

Explanation:

+ operator concatenates l1 and l2 into a single list.
sort() function rearranges the elements of the combined list in ascending order.

Using `heapq.merge()`

This method uses the merge() function from Python's heapq module which merges two sorted iterables into a single sorted iterable. The lists are first individually sorted then merged using heapq.merge().

import heapq

a = [25, 18, 9, 41, 26, 31]
b = [25, 45, 3, 32, 15, 20]

# Merge and sort using heapq.merge()
a.sort() 
b.sort()  
res = list(heapq.merge(a,b))

print(res)

 
import heapq
​a = [25, 18, 9, 41, 26, 31]b = [25, 45, 3, 32, 15, 20]​# Merge and sort using heapq.merge()a.sort() b.sort()  res = list(heapq.merge(a,b))​print(res)

Output

[3, 9, 15, 18, 20, 25, 25, 26, 31, 32, 41, 45]

Explanation:

Input lists (a and b) are sorted individually using sort().
heapq.merge() function combines the two sorted lists into a single sorted iterable which is converted to a list using list().

Creating a Sorted Merged List of Two Unsorted Lists in Python

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