Python – Append Multiple elements in set

In Python, sets are an unordered and mutable collection of data type what does not contains any duplicate elements. In this article, we will learn how to append multiple elements in the set at once.

Example:

Input: test_set = {6, 4, 2, 7, 9}, up_ele = [1, 5, 10]
Output: {1, 2, 4, 5, 6, 7, 9, 10}
Explanation: All elements are updated and reordered. (5 at 3rd position).
 
Input: test_set = {6, 4, 2, 7, 9}, up_ele = [1, 5, 8]
Output: {1, 2, 4, 5, 6, 7, 8, 9, 10}
Explanation: All elements are updated and reordered. (8 at 7th position).

Append Multiple Elements in Set in Python

There are various ways by which we can append elements given in a list to a Set in Python. They are as follows:

Using update() Method

In this method, we will use Python‘s in-built set update() function to get all the elements in the list aligned with the existing set.

Python3

# initializing set
test_set = {6, 4, 2, 7, 9}

# printing original set
print("The original set is : " + str(test_set))

# initializing adding elements
up_ele = [1, 5, 10]

# update() appends element in set
# internally reorders
test_set.update(up_ele)

# printing result
print("Set after adding elements : " + str(test_set))

Output:

The original set is : {2, 4, 6, 7, 9}
Set after adding elements : {1, 2, 4, 5, 6, 7, 9, 10}

Using | Operator (Pipe Operator)

The pipe operator internally calls the union() function, which can be used to perform the task of updating the Python set with new elements. 

Python3

# initializing set
test_set = {6, 4, 2, 7, 9}

# printing original set
print("The original set is : " + str(test_set))

# initializing adding elements
up_ele = [1, 5, 10]

# | performing task of updating
test_set |= set(up_ele)

# printing result
print("Set after adding elements : " + str(test_set))

Output:

The original set is : {2, 4, 6, 7, 9}
Set after adding elements : {1, 2, 4, 5, 6, 7, 9, 10}

Using List Comprehension

Here, we will use the Python list comprehension method to append only those elements in a set that are not already present in it. Then we use the set() constructor to convert the list to a Python set.

Python3

# initializing set
test_set = {6, 4, 2, 7, 9}
test_list = list(test_set)

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

# initializing adding elements
up_ele = [1, 5, 10]

# adding elements to list using list comprehension
test_list += [ele for ele in up_ele if ele not in test_list]

# printing result
print("Set after adding elements : " + str(set(test_list)))
#This code is contributed by Vinay Pinjala.

Output:

The original set is : [2, 4, 6, 7, 9]
Set after adding elements : {1, 2, 4, 5, 6, 7, 9, 10}

Using reduce() Method

This approach uses the reduce() function from the functools module to apply a union operation between each element of a list and the set, resulting in a new set in Python. The reduce() function takes a lambda function and the union() function

Python3

# import functools
from functools import reduce

# initializing set
test_set = {6, 4, 2, 7, 9}

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

# initializing adding elements
up_ele = [1, 5, 10]

# using reduce and union function to append elements to set
result_set = reduce(lambda res, ele: res.union(set([ele])), up_ele, test_set)

# printing result
print("Set after adding elements : " + str(result_set))

Output:

The original list is : {2, 4, 6, 7, 9}
Set after adding elements : {1, 2, 4, 5, 6, 7, 9, 10}