I have a numpy array [0, 1, 1, 2, 2, 0, 1, ...] which only contains the numbers 0-k. I would like to create a new array that contains the n possible arrays of permutations of 0-k. A small example with k=2 and n=6:
a = [0, 1, 0, 2]
permute(a)
result = [[0, 1, 0, 2]
[0, 2, 0, 1]
[1, 0, 1, 2]
[2, 1, 2, 0]
[1, 2, 1, 0]
[2, 0, 2, 1]]
Does anyone have any ideas/solutions as to how one could achieve this?
Your a is what combinatorists call a multiset. The sympy library has various routines for working with them.
>>> from sympy.utilities.iterables import multiset_permutations
>>> import numpy as np
>>> a = np.array([0, 1, 0, 2])
>>> for p in multiset_permutations(a):
... p
...
[0, 0, 1, 2]
[0, 0, 2, 1]
[0, 1, 0, 2]
[0, 1, 2, 0]
[0, 2, 0, 1]
[0, 2, 1, 0]
[1, 0, 0, 2]
[1, 0, 2, 0]
[1, 2, 0, 0]
[2, 0, 0, 1]
[2, 0, 1, 0]
[2, 1, 0, 0]
if your permutations fit in the memory, you could store them in a set and thus only get the distinguishable permutations.
from itertools import permutations
a = [0, 1, 0, 2]
perms = set(permutations(a))
set(permutations(a)) is a 1-line implementation of your idea.The other answers don't answer the question, their output doesn't match the example. The question asked to apply all permutations of the values 0,1,2 in the array.
Here is one way to do this:
import numpy as np
from itertools import permutations
a = [0, 1, 0, 2]
ps = np.array(list(permutations([0,1,2])))
result = ps[:,a]
Result, matching the example in the question:
[[0 1 0 2]
[0 2 0 1]
[1 0 1 2]
[1 2 1 0]
[2 0 2 1]
[2 1 2 0]]
Explanation: The array ps is
[[0 1 2]
[0 2 1]
[1 0 2]
[1 2 0]
[2 0 1]
[2 1 0]]
And the line ps[:,[0,1,0,2]] will select the items 0, 1, 0, 2 for each row. See Integer array indexing
