Why min({1},{0}) returns {1}

Question

min() function should return the smallest of the numbers given. Then why

min({0},{1})

returns {0}, while

min({1},{0})

returns {1}?

My question would be why don't dictionaries behave similarly?.. — Ma0, Jun 08 '17 at 12:19
@Ev.Kounis In Python 3 `dict` is an unorderably type, but in Python 2, they are compared https://stackoverflow.com/questions/3484293/is-there-a-description-of-how-cmp-works-for-dict-objects-in-python-2 — Chris_Rands, Jun 08 '17 at 12:21

Bernhard · Answer 1 · 2017-06-08T12:24:17.627

7

In python sets are compared based on whether or not one is a subset of the other.

None is a subset of the other, so < gives False in all cases, so the first one is returned.

So {1}<{0} gives False just like {2}<{1} gives False and {2}<{3,4,5} gives False. However {1,2}<{1,3,2} gives True. This means there is no total order defined on sets.

edited Jun 08 '17 at 12:24

answered Jun 08 '17 at 12:15

Bernhard

2,084
2
20
33

3

this is inncorrect `min({1,3,4,5},{0,2})` returns `{1, 3, 4, 5}`, which is of the smaller size – harshil9968 Jun 08 '17 at 12:21
My original answer was indeed incorrect. I edited the answer to give the correct answer: Set compare based on `is_subset` relation. – Bernhard Jun 08 '17 at 12:22

score 5 · Answer 2 · edited Jun 20 '20 at 09:12

5

The comparison operators for sets check for "subset" not for numerical comparisons:

set < other

Test whether the set is a proper subset of other, that is, set <= other and set != other.

And both your sets are disjoint so {0} < {1} == False and {1} < {0} == False so it will always return the "first" set you put into min.

edited Jun 20 '20 at 09:12

Community

1
1

answered Jun 08 '17 at 12:18

MSeifert

145,886
38
333
352

gsamaras · Answer 3 · 2017-06-08T12:24:10.070

4

Because these are sets, not numbers.

Moreover, it should return {1}, not 1, as you can see here:

>>> min({0},{1})
set([0])
>>> min({1},{0})
set([1])

That means that it will return the set, not the number.

edited Jun 08 '17 at 12:24

answered Jun 08 '17 at 12:15

gsamaras

71,951
46
188
305

1

It isn't true that sets are compared by size - eg, `min({2,3, 4}, {1,2})` is `{2,3,4}`. – lvc Jun 08 '17 at 12:21
@lvc you are right, answer updated! =) Is it OK now? – gsamaras Jun 08 '17 at 12:22
1

I believe it's better to paste code instead of image, it would be more readable. – vishes_shell Jun 08 '17 at 12:23
@vishes_shell you got it! – gsamaras Jun 08 '17 at 12:24

Why min({1},{0}) returns {1}

3 Answers3