Python | Check if all elements in a list are identical

Given a list, write a Python program to check if all the elements in that list are identical using Python. 

Examples:

Input : ['a', 'b', 'c']
Output : False

Input : [1, 1, 1, 1]
Output : True

Check if all elements in a list are identical or not using a loop 

Start a Python for loop and check if the first element is identical to all other elements in the list. This approach takes O(n) time complexity.

Python3

# Python3 program to check if
# all elements in a list are identical
def check(list):
    return all(i == list[0] for i in list)

# Driver code
print(check(['a', 'b', 'c']))
print(check([1, 1, 1]))

Output:

False
True

Check if all elements in a list are identical or not using set()

Set Converting the given list into Python set. It removes all duplicate elements, If the resultant set size is less than or equal to 1 then the list contains all identical elements. 

Python3

# Python3 program to check if
# all elements in a list are identical
def check(list):
   return len(set(list)) == 1

# Driver code
print(check(['a', 'b', 'c']))
print(check([1, 1, 1]))

Output:

False
True

Check if all elements in a list are identical or not using count() 

By counting the number of times the first element occurs in the list, we can check if the count is equal to the size of the list or not. In simple words, check if the first element is repeated throughout the list or not. 

Python3

def check(list):
   return list.count(list[0]) == len(list)

# Driver code
print(check(['a', 'b', 'c']))
print(check([1, 1, 1]))

Output:

False
True

Check if all elements in a list are identical or not using the length

Another method is to take the first element and multiply it by the length of the given list to form a new list, So that the new list contains identical elements to the first elements of the given list size, and then compare it with the given list. 

Python3

def check(x):
    return x and [x[0]]*len(x) == x

# Driver code
print(check(['a', 'b', 'c']))
print(check([1, 1, 1]))

Output:

False
True

Check if all elements in a list are identical or not using slicing

Python slice notation is used to retrieve a subset of values. Thus, we compare the start to the end of the list to the end to the start of the list. 

Python3

def check(list):
   return list[1:] == list[:-1]

# Driver code
print(check(['a', 'b', 'c']))
print(check([1, 1, 1]))

Output:

False
True

Check if all elements in a list are identical or not using itertools

Here is another approach that you can use to check if all the elements in a list are identical, using the repeat() function from the itertools module:

• Import the repeat() function from the itertools module.
• Use the repeat() function to generate an iterator that returns the first element of the list repeated len(lst) times.
• Convert the iterator to a list and compare it to the original list. If the lists are equal, return True, otherwise, return False.

Below is the code to implement the above approach:

Python3

from itertools import repeat

def check(lst):
    # Use the repeat function to generate an iterator that returns the first element of the list repeated len(lst) times
    repeated = list(repeat(lst[0], len(lst)))
    # Compare the repeated list to the original list and return the result
    return repeated == lst

# Test the function with different input lists
print(check(['a', 'b', 'c']))
print(check([1, 1, 1]))
print(check([1, 2, 3]))
print(check([1, 1, 1, 1, 1]))
#This code is contributed by Edula Vinay Kumar Reddy

Output

False
True
False
True

This approach has a time complexity of O(n) in the worst case, where n is the length of the list, because it involves iterating over the elements in the list and comparing them to the first element. The space complexity is O(n) because it involves creating a new list with a size proportional to the number of elements in the original list.

Approach#6: Using the itertools library

this approach uses the itertools library’s groupby() function to group the elements in the list by identity. If the resulting groups contain only one group, then all elements in the list are identical.

Algorithm

1. Import the itertools library
2. Use the groupby() function to group the elements in the list by identity
3. If the resulting groups contain only one group, then all elements in the list are identical
4. Return the result

Python3

import itertools


def check_identical(lst):
    groups = itertools.groupby(lst)
    return len(list(groups)) == 1


lst = ['a', 'b', 'c']
print(check_identical(lst))

lst = [1, 1, 1]
print(check_identical(lst))

Output

False

Time Complexity: O(n), where n is len of list.
Space Complexity: O(n), where n is len of list.

Approach#7: Uaing lambda

Using map() with an anonymous function to apply a comparison between the first element of the list and each of its elements, and then using all() to check if all comparisons return True.

Algorithm

1. Create a list of elements called data.
2. Create an anonymous function that compares its argument to the first element of data.
3. Use map() to apply the anonymous function to all elements of data.
4. Use all() to check if all the results of the map() function are True.
5. Print the result of the all() function.

Python3

data = [1,1,1,1]
result = all(map(lambda x: x == data[0], data))
print(result)

Output

True

Time Complexity: O(n), where n is the length of the list, because we have to iterate over the list once to compare all its elements or to create the set.

Auxiliary Space: O(n), where n is the length of the list, because we are creating an anonymous function and either a map or a set that contains all the elements of the list.