Python: Random from multiple lists, no repeats

Question

So say I have 4 lists of 10 different options each and I want to pick one item from each of the four lists a user specified amount of times. But no repeated outputs. Is this possible? I can't seem to write anything that will not repeat outputs.

Give an example of what you want to do. Its not very clear what you are trying to achieve. — Aditya, Apr 28 '13 at 19:37
See http://en.wikibooks.org/wiki/Python_Programming/Sets and http://stackoverflow.com/questions/1262955/how-do-i-pick-2-random-items-from-a-python-set . — Owen S., Apr 28 '13 at 21:51

score 2 · Answer 1 · answered Apr 28 '13 at 19:37

2

population = [1, 2, 3, 4, 5, 6, 5, 4, 3, 2, 1]
population = set(population)
samples = random.sample(population, 3)

answered Apr 28 '13 at 19:37

kiriloff

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score 2 · Accepted Answer · answered Apr 28 '13 at 19:47

Lets assume we have these 4 lists:

>>> lists = [range(10*i, 10*(i+1)) for i in range(4)]
>>> lists
[[0, 1, 2, 3, 4, 5, 6, 7, 8, 9], [10, 11, 12, 13, 14, 15, 16, 17, 18, 19], [20, 21, 22, 23, 24, 25, 26, 27, 28, 29], [30, 31, 32, 33, 34, 35, 36, 37, 38, 39]]

First of all, shuffle them:

>>> for lst in lists: random.shuffle(lst)

>>> lists
[[6, 8, 2, 1, 3, 5, 9, 0, 7, 4], [17, 12, 16, 10, 14, 15, 18, 11, 13, 19], [20, 28, 23, 21, 27, 25, 24, 29, 26, 22], [35, 32, 38, 31, 39, 34, 30, 33, 36, 37]]

And then output the values with zip:

>>> for items in zip(*lists):
    print(items)


(6, 17, 20, 35)
(8, 12, 28, 32)
(2, 16, 23, 38)
(1, 10, 21, 31)
(3, 14, 27, 39)
(5, 15, 25, 34)
(9, 18, 24, 30)
(0, 11, 29, 33)
(7, 13, 26, 36)
(4, 19, 22, 37)

If you need only the specified amount of them, just use islice:

>>> from itertools import islice
>>> for items in islice(zip(*lists),5):
    print(items)


(6, 17, 20, 35)
(8, 12, 28, 32)
(2, 16, 23, 38)
(1, 10, 21, 31)
(3, 14, 27, 39)

score 0 · Answer 3 · answered Apr 28 '13 at 19:40

Something like this should work:

a,b,c,d = initialize_lists()
output_picked_before = set()
n = number_of_experiments()

for i in range(n):
    t = pick_random_combination_from_list(a,b,c,d)
    while t in output_picked_before:
        t = pick_random_combination_from_list(a,b,c,d)
    print t
    output_picked_before.add(t)

Python: Random from multiple lists, no repeats

3 Answers3