How Can I Efficiently Check if All Elements in a Python List are Equal?

Checking Equality of List Elements

In Python, determining if all elements within a list are equal can be achieved using various approaches. One recommended method involves utilizing the itertools.groupby() function. This function groups consecutive elements with identical values, returning a sequence of tuples containing group keys (element values) and their respective groups.

from itertools import groupby

def all_equal(iterable):
    g = groupby(iterable)
    return next(g, True) and not next(g, False)

This code checks whether there's only one group within the list, indicating that all elements are equal. If that's the case, it returns True; otherwise, it returns False using the short-circuit evaluation property.

Alternately, you can use a more concise solution without groupby():

def all_equal(iterator):
    iterator = iter(iterator)
    try:
        first = next(iterator)
    except StopIteration:
        return True
    return all(first == x for x in iterator)

This approach initializes an iterator and retrieves the first element. Subsequently, it iterates over the remaining elements, comparing them to the first. If any difference is encountered, the function returns False; otherwise, it returns True.

While these methods are efficient, there are alternative one-liners you can consider:

1. Convert to a Set: Check if the length of the resultant set is less than or equal to 1.
2. Compare to the First Item: Compare the list to a list containing only the first item repeated.
3. Count Occurrences of First Item: Check if the count of the first item in the list is equal to the list's length.

These alternatives may be less memory-intensive and yield different performance characteristics. However, it's important to consider their limitations, such as potential memory copies and varying efficiency depending on the list's nature.

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