How to split a list into subsets with no repeating elements in python

Question

I need code that takes a list (up to n=31) and returns all possible subsets of n=3 without any two elements repeating in the same subset twice (think of people who are teaming up in groups of 3 with new people every time):

list=[1,2,3,4,5,6,7,8,9]

and returns

[1,2,3][4,5,6][7,8,9]

[1,4,7][2,3,8][3,6,9]

[1,6,8][2,4,9][3,5,7]

but not:

[1,5,7][2,4,8][3,6,9] 

because 1 and 7 have appeared together already (likewise, 3 and 9).

I would also like to do this for subsets of n=2. Thank you!!

Answer 1

Here's what I came up with:

from itertools import permutations, combinations, ifilter, chain

people = [1,2,3,4,5,6,7,8,9]

#get all combinations of 3 sets of 3 people
combos_combos = combinations(combinations(people,3), 3)

#filter out sets that don't contain all 9 people
valid_sets = ifilter(lambda combo: 
                     len(set(chain.from_iterable(combo))) == 9,
                     combos_combos)

#a set of people that have already been paired
already_together = set()
for sets in valid_sets:
    #get all (sorted) combinations of pairings in this set
    pairings = list(chain.from_iterable(combinations(combo, 2) for combo in sets))
    pairings = set(map(tuple, map(sorted, pairings)))

    #if all of the pairings have never been paired before, we have a new one
    if len(pairings.intersection(already_together)) == 0:
        print sets
        already_together.update(pairings)

This prints:

~$ time python test_combos.py 
((1, 2, 3), (4, 5, 6), (7, 8, 9))
((1, 4, 7), (2, 5, 8), (3, 6, 9))
((1, 5, 9), (2, 6, 7), (3, 4, 8))
((1, 6, 8), (2, 4, 9), (3, 5, 7))

real        0m0.182s
user        0m0.164s
sys         0m0.012s

Answer 2

Try this:

from itertools import permutations

lst = list(range(1, 10))

n = 3
triplets = list(permutations(lst, n))
triplets = [set(x) for x in triplets]

def array_unique(seq):  
    checked = [] 
    for x in seq:
        if x not in checked: 
            checked.append(x) 
    return checked

triplets = array_unique(triplets)

result = []
m = n * 3
for x in triplets:
    for y in triplets:
        for z in triplets:
            if len(x.union(y.union(z))) == m:
                result += [[x, y, z]]

def groups(sets, i):
    result = [sets[i]]

    for x in sets:
        flag = True
        for y in result:
            for r in x:
                for p in y:
                    if len(r.intersection(p)) >= 2:
                        flag = False
                        break
                    else:
                        continue
                if flag == False:
                    break
        if flag == True:
            result.append(x)

    return result

for i in range(len(result)):
    print('%d:' % (i + 1))
    for x in groups(result, i):
        print(x)

Output for n = 10: http://pastebin.com/Vm54HRq3