Get a list of the 1-element swap from an array in Python

Question

From a given array I need a list of all the 1-element-swap list. I dont know how is this called so better if I explain it with an example.

For example. For a given array :

array = [1,2,3,4]

I need the output:

[2,1,3,4]
[3,2,1,4]
[4,2,3,1]
[1,3,2,4]
[1,4,3,2]
[1,2,4,3]

This means if K is the size of the array, I must get a (K(K-1))/2 output arrays.

In the example above, K=4 so 4(3)/2=6 output arrays.

I really dont know how to do it. I know there's the itertools function, but if I use itertools.permutations(array) I don't get my desired solution as this shows me all the permutations, and I only need a list of the "1 swap element" list.

Have you tried simply looping through the values and swapping each of them with all other values? And then removing doubles obviously. — Martijn Arts
– Martijn Arts, Commented Apr 13, 2015 at 15:27

twalberg · Accepted Answer · 2015-04-13 15:33:46Z

2

Something like this should get you started:

>>> x = [1,2,3,4]
>>> for i in xrange(len(x)):
...     for j in xrange(i + 1, len(x)):
...         y = x[:]
...         y[i], y[j] = y[j], y[i]
...         print y
...

answered Apr 13, 2015 at 15:33

twalberg

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1 Comment

Algorithmic Canary Over a year ago

If you are using python 3 replace xrange with range, and print y with print(y);

njzk2 · Accepted Answer · 2015-04-13 15:37:44Z

0

Quite simply:

array = [1,2,3,4]

# swaps to elements, and return the resulting array
def swap(x, i, j):
    x[i], x[j] = x[j], x[i]
    return x

arrays = [swap(array[:], i, j) 
                 for i in range(len(array))
                 for j in range(i + 1, len(array))]

print(arrays)

answered Apr 13, 2015 at 15:37

njzk2

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