CODEWITHSUNDEEP
pythonpython-2.7
Devang
Devang

Reputation: 55

Python permutations in order

listA = ["A","B","C","D"]

From this, I want the following output only:

["A","B","C"]
["B","C","D"]
["C","D","A"]
["D","A","B"]

I have looked at various questions on permutations here, but I am not able to do achieve this so far. Any help will be appreciated.

Upvotes: 2

Views: 3610

Answers (3)

Devang
Devang

Reputation: 55

Thanks for all your answers. I received one another answer from a friend that I wanted to share here. It goes like this.

listA = ["A","B","C","D"]
listB = listA + [listA[0]] + [listA[1]]

catch = []
for i in range(len(listA)):
    A = listB[i]
    B = listB[i+1]
    C = listB[i+2]
    catch.append([A,B,C])
print catch

Upvotes: 0

Chris_Rands
Chris_Rands

Reputation: 41168

You could use itertools.cycle and itertools.islice.

To get the order you show (as @tobias_k suggested):

>>> from itertools import cycle, islice
>>> listA = ["A","B","C","D"]
>>> [list(islice(cycle(listA), i, i+3)) for i in range(len(listA))]
[['A', 'B', 'C'], ['B', 'C', 'D'], ['C', 'D', 'A'], ['D', 'A', 'B']]

To get an alternative sequential ordering:

>>> it = cycle(listA)
>>> [list(islice(it,3)) for _ in range(len(listA))]
[['A', 'B', 'C'], ['D', 'A', 'B'], ['C', 'D', 'A'], ['B', 'C', 'D']]

Upvotes: 3

Rehan Shikkalgar
Rehan Shikkalgar

Reputation: 1047

another way to do this - brute force,

def permutation(L):
    for i in range(len(L)):
        x = L[i:i+3]
        length = len(x)
        if length != 3:
            x = x + L[:3-length]
        print(x)


L = ["A","B","C","D"]
permutation(L)

Upvotes: 3

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