how to generate combinations with no repetitions of characters in python?

Question

I have the following charset:

qwertyiopnmjk013

I want to generate all possible strings of 6 characters and also all with 7 characters noting that each letter only appears once in the same generated string.

Which is the best form to do it in python? Any example?

Right now I'm copying the charset to another variable and then I start generating picking letters and removing them from the charset then moving forward but I think that's not the best way..

This is not a duplicate. Since he is asking for "all possible strings" he means permutations, not combinations as the title suggests. — Imran, Dec 14 '17 at 18:27

score 3 · Answer 1 · answered Dec 14 '17 at 00:47

3

use itertools:

    import itertools
    myStr = "qwertyiopnmjk013"
    chars = list(myStr)
    for comb in itertools.combinations(chars, 6):
        print comb

answered Dec 14 '17 at 00:47

Austin A

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What about this "Noting that each letter only appears once in the same generated string."? – Axalix Dec 14 '17 at 00:50
That's part of the standard mathematical definition of "combination". – Lee Daniel Crocker Dec 14 '17 at 00:51
@LeeDanielCrocker that's not a part of a question. It was said "appears once" – Axalix Dec 14 '17 at 00:53
1

You can check the chars list for uniqueness before calling combinations() and make any appropriate changes such as removing duplicates. – Austin A Dec 14 '17 at 00:54
Yes, what I'm saying is that the way he asked the question is compatible with the standard definition of "combination", so the combinations() function does exactly what he asked for. – Lee Daniel Crocker Dec 14 '17 at 00:54
He didn't say anything about the input string, only the generated ones. – Lee Daniel Crocker Dec 14 '17 at 00:55
@LeeDanielCrocker `print(list(itertools.combinations(list("aaaa"), 2)))` prints out `[('a', 'a'), ('a', 'a'), ('a', 'a'), ('a', 'a'), ('a', 'a'), ('a', 'a')]` – Axalix Dec 14 '17 at 00:56
Yes it does. If he wants to uniquify his input string, he can do that as well. – Lee Daniel Crocker Dec 14 '17 at 00:59

Lee Daniel Crocker · Answer 2 · 2017-12-14T01:44:51.017

2

The question is somewhat ambiguous, but here's all the parts. First, just to get combinations:

import itertools
source = "qwertyiopnmjk013"
map(''.join, itertools.combinations(source, 6))

Now, if you want no repeated letters even if your source string contains duplicates, then fix your source string first with:

source = ''.join(set("qwertyiopnmjk013"))

If you also want each of the combinations re-arranged in each order, then you're dealing with permutations, not combinations. To get both into a nice list:

reduce(lambda x, y: x + y, map(lambda x: map(''.join, itertools.permutations(x)), itertools.combinations(source, 6)))

You should note that at this point you're getting into 10s of millions of strings; hope you have a fast machine.

edited Dec 14 '17 at 01:44

answered Dec 14 '17 at 00:50

Lee Daniel Crocker

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`import itertools print(map("".join, itertools.combinations("aaaaaaa", 6)))` => `['aaaaaa', 'aaaaaa', 'aaaaaa', 'aaaaaa', 'aaaaaa', 'aaaaaa', 'aaaaaa']` Task: noting that *each letter only appears once in the same generated string*. I think the issue is in considering same letters in the original string as "different". I admit the question can be read differently and there's some ambitiously. – Axalix Dec 14 '17 at 01:00

score 0 · Answer 3 · answered Dec 14 '17 at 00:52

0

You can use itertools.combinations:

import itertools
s = "qwertyiopnmjk013"
final_letters = [''.join(b) for b in [i for i in itertools.combinations(s, 6)]+[i for i in itertools.combinations(s, 7)] if len(set(b)) == len(b)]

answered Dec 14 '17 at 00:52

Ajax1234

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score 0 · Answer 4 · answered Dec 14 '17 at 00:56

Since you say:

I want to generate all possible strings of 6 characters and also all with 7 characters noting that each letter only appears once in the same generated string.

I assume you mean permutations, not combinations.

In your example you don't have repeated characters, but in case you do you can convert the string to a set first.

from itertools import permutations

def permute_string(s, n):
    return map(lambda x: ''.join(x), permutations(set(s)))

my_string = 'qwertyiopnmjk013'
six_chars = list(permute_string(my_string, 6))
seven_chars = list(permute_string(my_string, 7))

how to generate combinations with no repetitions of characters in python?

4 Answers4