Remove multiple elements from a list in Python

Last Updated : 29 Apr, 2023

Given a list of numbers, write a Python program to remove multiple elements from a list based on the given condition.

Example:

Input: [12, 15, 3, 10]
Output: Remove = [12, 3], New_List = [15, 10]

Input: [11, 5, 17, 18, 23, 50]
Output: Remove = [1:5], New_list = [11, 50]

Multiple elements can be deleted from a list in Python, based on the knowledge we have about the data. Like, we just know the values to be deleted or also know the indexes of those values. Let’s see different examples based on a different scenarios.

Example #1: Let’s say we want to delete each element in the list which is divisible by 2 or all the even numbers.

Python3

# Python program to remove multiple
# elements from a list 
 
# creating a list
list1 = [11, 5, 17, 18, 23, 50] 
 
# Iterate each element in list
# and add them in variable total
for ele in list1:
    if ele % 2 == 0:
        list1.remove(ele)
 
# printing modified list
print("New list after removing all even numbers: ", list1)

Output:

New list after removing all even numbers:  [11, 5, 17, 23]

Time Complexity: O(n)
Auxiliary Space: O(n)

Example #2: Using list comprehension

Removing all even elements in a list is as good as only including all the elements which are not even( i.e. odd elements).

Python3

# Python program to remove multiple
# elements from a list 
 
# creating a list
list1 = [11, 5, 17, 18, 23, 50] 
 
# will create a new list, 
# excluding all even numbers
list1 = [ elem for elem in list1 if elem % 2 != 0]
 
print(*list1)

Output:

11 5 17 23

Time Complexity: O(n)
Auxiliary Space: O(n)

Example #3: Remove adjacent elements using list slicing

Below Python code remove values from index 1 to 4.

Python3

# Python program to remove multiple
# elements from a list 
 
# creating a list
list1 = [11, 5, 17, 18, 23, 50] 
 
# removes elements from index 1 to 4
# i.e. 5, 17, 18, 23 will be deleted
del list1[1:5]
 
print(*list1)

Output:

11 50

Time Complexity: O(n)
Auxiliary Space: O(n)

Example #4: Using list comprehension

Let’s say the elements to be deleted is known, instead of the indexes of those elements. In this case, we can directly eliminate those elements without caring about indexes which we will see in next example.

Python3

# Python program to remove multiple
# elements from a list 
 
# creating a list
list1 = [11, 5, 17, 18, 23, 50] 
 
# items to be removed
unwanted_num = {11, 5}
 
list1 = [ele for ele in list1 if ele not in unwanted_num]
 
# printing modified list
print("New list after removing unwanted numbers: ", list1)

Output:

New list after removing unwanted numbers:  [17, 18, 23, 50]

Time Complexity: O(n)
Auxiliary Space: O(n)

Example #5: When index of elements is known.
Though indexes of elements in known, deleting the elements randomly will change the values of indexes. Hence, it is always recommended to delete the largest indices first. Using this strategy, index of smaller values will not be changed. We can sort the list in reverse order and delete the elements of list in descending order.

Python3

# Python program to remove multiple
# elements from a list 
 
# creating a list
list1 = [11, 5, 17, 18, 23, 50] 
 
# given index of elements 
# removes 11, 18, 23
unwanted = [0, 3, 4]
 
for ele in sorted(unwanted, reverse = True): 
    del list1[ele]
 
# printing modified list
print (*list1)

Output:

5 17 50

Method: Using enumerate function

Python3

list1 = [11, 5, 17, 18, 23, 50] 
 
list1 = [ elem for i,elem in enumerate(list1) if elem % 2 != 0]
 
print(list1)

Output

[11, 5, 17, 23]

Time Complexity: O(n log n)
Auxiliary Space: O(n)

Approach using numpy.delete():

Algorithm:

Create a numpy array from the given list.
Find the indices of the elements to be removed.
Use numpy.delete() to remove the elements based on the indices found in the previous step.
Convert the resulting numpy array back to a list.
Code:

Python3

import numpy as np
 
#creating a list
list1 = [12, 15, 3, 10]
 
#convert list to numpy array
arr = np.array(list1)
 
#indices of elements to be removed
remove_idx = [0, 2]
 
#use numpy.delete() to remove elements
new_arr = np.delete(arr, remove_idx)
 
#convert numpy array back to list
new_list = new_arr.tolist()
 
#print the results
print("Removed =", [list1[i] for i in remove_idx], ", New_List =", new_list)

Output;

Removed = [12, 3] , New_List = [15, 10]

Time complexity: O(n)
Space complexity: O(n) (for creating the numpy array)

S

Shivam_k

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