Python - Check if all elements in List are same

To check if all items in list are same, we have multiple methods available in Python.

Using Set

Using set() is the best method to check if all items are same in list.

a = [3, 3, 3, 3]

# Check if all elements are the same
result = len(set(a)) == 1
print(result)

True

Explanation:

• Converting given list to set will take O(n) time, because we are adding each item in set.
• In Set, checking length can be done in O(1) constant time.

Let's explore some other methods and see how we can check if all elements in a list are same or not.

Using all() method

all() function checks if all elements in an iterable meet a condition. By comparing each element to the first list we can confirm if the entire list is uniform.

#Driver Code Starts
a = [5, 5, 5, 5]

#Driver Code Ends

# Check if all elements are the same
result = all(x == a[0] for x in a)

#Driver Code Starts
print(result)

#Driver Code Ends

True

Using all() method can be preferred, as it stops iterating once it finds any mismatched item during comparison.

Explanation:

• x == a[0] for x in a : For each iteration, it checks if the current element x is equal to the first element of the list (a[0] which is 5 in this case)
• all() function takes above generator and checks if all values evaluates to True.

Using count() method

count() method will iterate over the entire list to count the occurrence of first item.

a = [5, 5, 5, 5]

# count the occurence of first element
res = a.count(a[0]) == len(a)

print(res)

True

Explanation:

• a.count(a[0]) counts how many times the first element appears in the list.
• this result is compared with length of list using len(a)
• If both are same, above code will return True, else False.

Using For Loop

A simple loop iterates through the list and checks if all elements are equal to the first element. This approach is easy to understand and implement.

a = [1, 1, 1, 1]

# Check if all elements are the same
result = True

for x in a:
    if x != a[0]:
        result = False
        break

print( result)

True

Explanation:

• The loop compares each element to the first.
• If a mismatch is found the result is set to False and the loop exits

Using List Slicing

This approach compares all elements in the list to the first element using slicing. It’s concise and effective for short lists and comparing these ensures uniformity.

#Driver Code Starts
a = [2, 2, 2, 2]

#Driver Code Ends

# Check if all elements are the same
result = a[1:] == a[:-1]

#Driver Code Starts
print(result)

#Driver Code Ends

True

Explanation:

• a[1:] contains all elements except the first.
• a[:-1] contains all elements except the last.
• If a[1:] and a[:-1] are same, it means all elements in the original list are the same.

Note: We should avoid using this method if the list could be empty or contain only one element, as it may give misleading results.