How to check if every element in list are equal?

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check if all elements in a list are identical

I want to check if all of the elements of a list are equal. I couldn't do this with:

if all (x == x for x in (a, b, c, d)):
    ...

Is there very minimalistic and elegant way to do this in Python?

http://stackoverflow.com/questions/3844801/check-if-all-elements-in-a-list-are-identical — The Unfun Cat, Oct 29 '12 at 17:43
Are you not just comparing each element to itself here? When would an element not be equal to itself? — Felix Kling, Oct 29 '12 at 17:43
@Eric: Good call, didn't remember anymore whether `NaN` exists in Python. — Felix Kling, Oct 29 '12 at 18:29

enrico.bacis · Accepted Answer · 2012-10-29T17:52:35.053

5

If you have only hashable elements in your list you can use a set.

For example if your list is named lst you can do:

if (len(set(lst)) <= 1):
    ....

The set will eliminate all the duplicates in your list, so if the length of the set is 1 it means that all the elements are the same.

edited Oct 29 '12 at 17:52

answered Oct 29 '12 at 17:44

enrico.bacis

1

This will fail if the items in the list aren't hashable. – Zero Piraeus Oct 29 '12 at 17:47
True, I don't know why but I assumed he was going to compare numbers, I'll edit the answer. Thanks – enrico.bacis Oct 29 '12 at 17:51

score 3 · Answer 2 · answered Oct 29 '12 at 17:44

3

all(x == items[0] for x in items)

this is what you're looking for.

Otherwise you would be comparing every value to itself x==x as opposed to every value to the first value.

answered Oct 29 '12 at 17:44

John

Joran Beasley · Answer 3 · 2012-10-29T17:49:50.153

0

first = my_list[0]
print all(x==first for x in my_list[1:])

should work

more elegant maybe ... (I dont really think so...)

>>> if reduce(lambda item0,item1:item0 if item0==item1 else False,my_list) is not False:
...    print "OK ALL THE SAME!"
...
OK ALL THE SAME!

edited Oct 29 '12 at 17:49

answered Oct 29 '12 at 17:43

Joran Beasley

Could you please explain how this works? – Berk Özbalcı Oct 29 '12 at 17:44
reduce applies a function to every pair of elements in the list shrinking it until there is only a scalar value left .. bah reduce didnt work ... ill see if i can get a version working with reduce – Joran Beasley Oct 29 '12 at 17:48

score -2 · Answer 4 · edited May 23 '17 at 12:34

-2

answered here , with performance benchmark

my favorite : lst[1:] == lst[:-1]

edited May 23 '17 at 12:34

Community

answered Oct 29 '12 at 17:46

lucasg

2

Then please vote to close / flag this question as duplicate and don't copy answers. – Felix Kling Oct 29 '12 at 17:47

4 Answers4