Python itertools permutations with double elements

Question

I'm using python (2.7.2) and I need all permutations without repetition from a list. More precisely,

 for i in itertools.permutations([1,2,3]): print i

correctly gives

(1, 2, 3)
(1, 3, 2)
(2, 1, 3)
(2, 3, 1)
(3, 1, 2)
(3, 2, 1)

But now I am looking for something would do the following

for i in myfunction([1,2,2]): print i
(1,2,2)
(2,2,1)
(2,1,2)

Whereas itertools would give that list twice (or, for ([1,1,1]) as the input, it is just repeated six times). This is basically something between itertools.permutations and itertools.combinations. I tried working with sets, but all solutions that I tried always created new problems and never matched the desired output.

Can't you just filter the result through a `set`? `for i in set(itertools.permutations([1,2,2])): print i` — tobias_k, Oct 27 '16 at 15:33
Works. Thanks, somehow failed to get there in the beginning and ended up in way to complicated solutions. — Eulenfuchswiesel, Oct 27 '16 at 15:41
There's an efficient way to do that in [this old answer of mine](http://stackoverflow.com/a/31678111/4014959) — PM 2Ring, Oct 27 '16 at 15:47
Impressive algorithm, but way above the demands of my program. — Eulenfuchswiesel, Oct 27 '16 at 15:52
I'll add a modified version of that code here, since that question is somewhat different to yours. — PM 2Ring, Oct 27 '16 at 15:52
The sympy library has an iterator for this. Please see my answer (just added) in the question that @tobias_k just referenced. — Bill Bell, Oct 27 '16 at 16:29

Andy · Accepted Answer · 2016-10-27T15:39:01.027

3

It looks like you want the set.

s = []
for i in itertools.permutations([1,2,2]):
    s.append(i)
print(set(s))

Which gives:

{(1, 2, 2), (2, 2, 1), (2, 1, 2)}

Alternatively, without saving the objects to a variable:

for i in set(itertools.permutations([1,2,2])):
    print(i)

edited Oct 27 '16 at 15:39

answered Oct 27 '16 at 15:37

Andy

134
8

1

Is there any reason you don't just insert directly into the set? What is the purpose of the list? – Mad Physicist Oct 27 '16 at 15:38
I edited my response to include the direct method but the reason was to show how keep an object with the desired information. – Andy Oct 27 '16 at 15:40
Why would you need to save the objects? – Mad Physicist Oct 27 '16 at 15:41

Python itertools permutations with double elements

1 Answers1