changing a permutation into combinations (PYTHON)

Question

I made the mistake of using permutations instead of combinations, i am supposed to print the names the user enters in this programs in pairs of two, not all the permutations of the names together, here is a snippet of my code, the full code can be found HERE So the general question is instead of printing out every name combination possible, how can i print non repeated pairs of 2?

names = []

for i in range(n): names.append(raw_input("Enter name " + str(i + 1) + ": "))

count = 0


def perm(a, k=0):
global count
if (k == len(a)):
    print a

    count += 1
 else:
    for i in xrange(k, len(a)):
        a[k], a[i] = a[i], a[k]
        perm(a, k + 1)
        a[k], a[i] = a[i], a[k]


if n % 2 == 0:
print""
perm(names)
print"total combinations available: " + str(count)
else:

perm(names)
print"total combinations available: " + str(count)
print("please enter an even number next time")

sys.exit()

@leaf how exactly would i go about with this? delete everything between "for i" up to the "for" statement and replace it? sorry im really noobie — ethan jjjjjj
– ethan jjjjjj, Commented Dec 14, 2016 at 14:58

Chris · Accepted Answer · 2016-12-14 15:00:56Z

1

You can use itertools.combinations() to create all possible combinations, and then use set() to filter out all unique combinations:

import itertools
...
combinations = set(itertools.combinations(names, 2))

However, in your code it seems you only care about the number of possible combinations. You can use the builtin function len() to find this:

number_of_combinations = len(combinations)

Wherever you used count replace it with number_of_combinations.

answered Dec 14, 2016 at 15:00

Chris

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1 Comment

Chris Over a year ago

My pleasure, @ethanjjjjjj.

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